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Zambon P, Palani S, Jadhav SS, Gayathri P, Balasubramanian MK. Genetic suppression of defective profilin by attenuated Myosin II reveals a potential role for Myosin II in actin dynamics in vivo in fission yeast. Mol Biol Cell 2020; 31:2107-2114. [PMID: 32614646 PMCID: PMC7530902 DOI: 10.1091/mbc.e20-04-0224] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The actin cytoskeleton plays a variety of roles in eukaryotic cell physiology, ranging from cell polarity and migration to cytokinesis. Key to the function of the actin cytoskeleton is the mechanisms that control its assembly, stability, and turnover. Through genetic analyses in Schizosaccharomyces pombe, we found that myo2-S1 (myo2-G515D), a Myosin II mutant allele, was capable of rescuing lethality caused by partial defects in actin nucleation/stability caused, for example, through compromised function of the actin-binding protein Cdc3-profilin. The mutation in myo2-S1 affects the activation loop of Myosin II, which is involved in physical interaction with subdomain 1 of actin and in stimulating the ATPase activity of Myosin. Consistently, actomyosin rings in myo2-S1 cell ghosts were unstable and severely compromised in contraction on ATP addition. These studies strongly suggest a role for Myo2 in actin cytoskeletal disassembly and turnover in vivo, and that compromise of this activity leads to genetic suppression of mutants defective in actin filament assembly/stability at the division site.
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Affiliation(s)
- Paola Zambon
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Saravanan Palani
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Shekhar Sanjay Jadhav
- Biology Division, Indian Institute of Science Education and Research, Pune, Maharashtra 411008, India
| | - Pananghat Gayathri
- Biology Division, Indian Institute of Science Education and Research, Pune, Maharashtra 411008, India
| | - Mohan K Balasubramanian
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, United Kingdom
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2
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Dorweiler JE, Oddo MJ, Lyke DR, Reilly JA, Wisniewski BT, Davis EE, Kuborn AM, Merrill SJ, Manogaran AL. The actin cytoskeletal network plays a role in yeast prion transmission and contributes to prion stability. Mol Microbiol 2020; 114:480-494. [PMID: 32426863 DOI: 10.1111/mmi.14528] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 04/21/2020] [Accepted: 05/09/2020] [Indexed: 01/22/2023]
Abstract
Chaperone networks are required for the shearing and generation of transmissible propagons from pre-existing prion aggregates. However, other cellular networks needed for maintaining yeast prions are largely uncharacterized. Here, we establish a novel role for actin networks in prion maintenance. The [PIN+ ] prion, also known as [RNQ+ ], exists as stable variants dependent upon the chaperone machinery for the transmission of propagons to daughter cells during cell division and cytoplasmic transfer. Loss of the Hsp104 molecular chaperone leads to the growth of prion particles until they are too large to be transmitted. Here, we isolated a unique [PIN+ ] variant, which is unstable in actin mutants. This prion loss is observed over many generations, and coincides with the detection of both high molecular weight species of Rnq1 and large visible aggregates that are asymmetrically retained during cell division. Our data suggest that the irregular actin networks found in these mutants may influence propagon number by slowly permitting aggregate growth over time, resulting in the generation of nontransmissible large aggregates. Thus, we show the potential contribution of cytoskeletal networks in the transmission of prion propagons, which parallels models that have been proposed for cell-to-cell transmission of small amyloids in neurodegenerative protein aggregation diseases.
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Affiliation(s)
- Jane E Dorweiler
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Mitchell J Oddo
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Douglas R Lyke
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Jacob A Reilly
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Brett T Wisniewski
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Emily E Davis
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Abigail M Kuborn
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Stephen J Merrill
- Department of Mathematical and Statistical Sciences, Marquette University, Milwaukee, WI, USA
| | - Anita L Manogaran
- Department of Biological Sciences, Marquette University, Milwaukee, WI, USA
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3
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Christensen JR, Homa KE, Morganthaler AN, Brown RR, Suarez C, Harker AJ, O'Connell ME, Kovar DR. Cooperation between tropomyosin and α-actinin inhibits fimbrin association with actin filament networks in fission yeast. eLife 2019; 8:47279. [PMID: 31180322 PMCID: PMC6557641 DOI: 10.7554/elife.47279] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2019] [Accepted: 05/29/2019] [Indexed: 11/13/2022] Open
Abstract
We previously discovered that competition between fission yeast actin binding proteins (ABPs) for binding F-actin facilitates their sorting to different cellular networks. Specifically, competition between endocytic actin patch ABPs fimbrin Fim1 and cofilin Adf1 enhances their activities, and prevents tropomyosin Cdc8's association with actin patches. However, these interactions do not explain how Fim1 is prevented from associating strongly with other F-actin networks such as the contractile ring. Here, we identified α-actinin Ain1, a contractile ring ABP, as another Fim1 competitor. Fim1 competes with Ain1 for association with F-actin, which is dependent upon their F-actin residence time. While Fim1 outcompetes both Ain1 and Cdc8 individually, Cdc8 enhances the F-actin bundling activity of Ain1, allowing Ain1 to generate F-actin bundles that Cdc8 can bind in the presence of Fim1. Therefore, the combination of contractile ring ABPs Ain1 and Cdc8 is capable of inhibiting Fim1's association with F-actin networks.
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Affiliation(s)
- Jenna R Christensen
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Kaitlin E Homa
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Alisha N Morganthaler
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Rachel R Brown
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Cristian Suarez
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Alyssa J Harker
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States
| | - Meghan E O'Connell
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States.,Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States
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4
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Miao Y, Han X, Zheng L, Xie Y, Mu Y, Yates JR, Drubin DG. Fimbrin phosphorylation by metaphase Cdk1 regulates actin cable dynamics in budding yeast. Nat Commun 2016; 7:11265. [PMID: 27068241 PMCID: PMC4832064 DOI: 10.1038/ncomms11265] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 03/07/2016] [Indexed: 12/15/2022] Open
Abstract
Actin cables, composed of actin filament bundles nucleated by formins, mediate intracellular transport for cell polarity establishment and maintenance. We previously observed that metaphase cells preferentially promote actin cable assembly through cyclin-dependent kinase 1 (Cdk1) activity. However, the relevant metaphase Cdk1 targets were not known. Here we show that the highly conserved actin filament crosslinking protein fimbrin is a critical Cdk1 target for actin cable assembly regulation in budding yeast. Fimbrin is specifically phosphorylated on threonine 103 by the metaphase cyclin–Cdk1 complex, in vivo and in vitro. On the basis of conformational simulations, we suggest that this phosphorylation stabilizes fimbrin's N-terminal domain, and modulates actin filament binding to regulate actin cable assembly and stability in cells. Overall, this work identifies fimbrin as a key target for cell cycle regulation of actin cable assembly in budding yeast, and suggests an underlying mechanism. Metaphase cells preferentially promote actin cable assembly through cyclin-dependent kinase 1 (Cdk1) activity. Here the authors identify fimbrin as one of the main metaphase Cdk1 targets for cell cycle regulation of actin cable assembly in budding yeast.
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Affiliation(s)
- Yansong Miao
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202, USA.,School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore.,School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore
| | - Xuemei Han
- Department of Chemical Physiology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Liangzhen Zheng
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - Ying Xie
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore
| | - Yuguang Mu
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - John R Yates
- Department of Chemical Physiology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - David G Drubin
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202, USA
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5
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Rubenstein PA, Wen KK. Insights into the effects of disease-causing mutations in human actins. Cytoskeleton (Hoboken) 2014; 71:211-29. [PMID: 24574087 DOI: 10.1002/cm.21169] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 02/13/2013] [Accepted: 02/19/2014] [Indexed: 01/04/2023]
Abstract
Mutations in all six actins in humans have now been shown to cause diseases. However, a number of factors have made it difficult to gain insight into how the changes in actin functions brought about by these pathogenic mutations result in the disease phenotype. These include the presence of multiple actins in the same cell, limited accessibility to pure mutant material, and complexities associated with the structures and their component cells that manifest the diseases. To try to circumvent these difficulties, investigators have turned to the use of model systems. This review describes these various approaches, the initial results obtained using them, and the insight they have provided into allosteric mechanisms that govern actin function. Although results so far have not explained a particular disease phenotype at the molecular level, they have provided valuable insight into actin function at the mechanistic level which can be utilized in the future to delineate the molecular bases of these different actinopathies.
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Affiliation(s)
- Peter A Rubenstein
- Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, Iowa
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Waldmann H, Hu TS, Renner S, Menninger S, Tannert R, Oda T, Arndt HD. Total Synthesis of Chondramide C and Its Binding Mode to F-Actin. Angew Chem Int Ed Engl 2008; 47:6473-7. [DOI: 10.1002/anie.200801010] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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7
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Waldmann H, Hu TS, Renner S, Menninger S, Tannert R, Oda T, Arndt HD. Totalsynthese von Chondramid C und Bindung an F-Aktin. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200801010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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8
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Gheorghe DM, Aghamohammadzadeh S, Smaczynska-de Rooij II, Allwood EG, Winder SJ, Ayscough KR. Interactions between the yeast SM22 homologue Scp1 and actin demonstrate the importance of actin bundling in endocytosis. J Biol Chem 2008; 283:15037-46. [PMID: 18400761 PMCID: PMC2397485 DOI: 10.1074/jbc.m710332200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The yeast SM22 homologue Scp1 has previously been shown to act as an actin-bundling protein in vitro. In cells, Scp1 localizes to the cortical actin patches that form as part of the invagination process during endocytosis, and its function overlaps with that of the well characterized yeast fimbrin homologue Sac6p. In this work we have used live cell imaging to demonstrate the importance of key residues in the Scp1 actin interface. We have defined two actin binding domains within Scp1 that allow the protein to both bind and bundle actin without the need for dimerization. Green fluorescent protein-tagged mutants of Scp1 also indicate that actin localization does not require the putative phosphorylation site Ser-185 to be functional. Deletion of SCP1 has few discernable effects on cell growth and morphology. However, we reveal that scp1 deletion is compensated for by up-regulation of Sac6. Furthermore, Scp1 levels are increased in the absence of sac6. The presence of compensatory pathways to up-regulate Sac6 or Scp1 levels in the absence of the other suggest that maintenance of sufficient bundling activity is critical within the cell. Analysis of cortical patch assembly and movement during endocytosis reveals a previously undetected role for Scp1 in movement of patches away from the plasma membrane. Additionally, we observe a dramatic increase in patch lifetime in a strain lacking both sac6 and scp1, demonstrating the central role played by actin-bundling proteins in the endocytic process.
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Affiliation(s)
- Dana M Gheorghe
- Departments of Molecular Biology and Biotechnology, Biomedical Science, University of Sheffield, Sheffield, S10 2TN, United Kingdom
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9
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Moseley JB, Goode BL. The yeast actin cytoskeleton: from cellular function to biochemical mechanism. Microbiol Mol Biol Rev 2006; 70:605-45. [PMID: 16959963 PMCID: PMC1594590 DOI: 10.1128/mmbr.00013-06] [Citation(s) in RCA: 287] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
All cells undergo rapid remodeling of their actin networks to regulate such critical processes as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. These events are driven by the coordinated activities of a set of 20 to 30 highly conserved actin-associated proteins, in addition to many cell-specific actin-associated proteins and numerous upstream signaling molecules. The combined activities of these factors control with exquisite precision the spatial and temporal assembly of actin structures and ensure dynamic turnover of actin structures such that cells can rapidly alter their cytoskeletons in response to internal and external cues. One of the most exciting principles to emerge from the last decade of research on actin is that the assembly of architecturally diverse actin structures is governed by highly conserved machinery and mechanisms. With this realization, it has become apparent that pioneering efforts in budding yeast have contributed substantially to defining the universal mechanisms regulating actin dynamics in eukaryotes. In this review, we first describe the filamentous actin structures found in Saccharomyces cerevisiae (patches, cables, and rings) and their physiological functions, and then we discuss in detail the specific roles of actin-associated proteins and their biochemical mechanisms of action.
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Affiliation(s)
- James B Moseley
- Department of Biology and The Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA
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10
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Ren G, Vajjhala P, Lee JS, Winsor B, Munn AL. The BAR domain proteins: molding membranes in fission, fusion, and phagy. Microbiol Mol Biol Rev 2006; 70:37-120. [PMID: 16524918 PMCID: PMC1393252 DOI: 10.1128/mmbr.70.1.37-120.2006] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The Bin1/amphiphysin/Rvs167 (BAR) domain proteins are a ubiquitous protein family. Genes encoding members of this family have not yet been found in the genomes of prokaryotes, but within eukaryotes, BAR domain proteins are found universally from unicellular eukaryotes such as yeast through to plants, insects, and vertebrates. BAR domain proteins share an N-terminal BAR domain with a high propensity to adopt alpha-helical structure and engage in coiled-coil interactions with other proteins. BAR domain proteins are implicated in processes as fundamental and diverse as fission of synaptic vesicles, cell polarity, endocytosis, regulation of the actin cytoskeleton, transcriptional repression, cell-cell fusion, signal transduction, apoptosis, secretory vesicle fusion, excitation-contraction coupling, learning and memory, tissue differentiation, ion flux across membranes, and tumor suppression. What has been lacking is a molecular understanding of the role of the BAR domain protein in each process. The three-dimensional structure of the BAR domain has now been determined and valuable insight has been gained in understanding the interactions of BAR domains with membranes. The cellular roles of BAR domain proteins, characterized over the past decade in cells as distinct as yeasts, neurons, and myocytes, can now be understood in terms of a fundamental molecular function of all BAR domain proteins: to sense membrane curvature, to bind GTPases, and to mold a diversity of cellular membranes.
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Affiliation(s)
- Gang Ren
- Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia
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11
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Clark SW, Rose MD. Alanine scanning of Arp1 delineates a putative binding site for Jnm1/dynamitin and Nip100/p150Glued. Mol Biol Cell 2005; 16:3999-4012. [PMID: 15975903 PMCID: PMC1196314 DOI: 10.1091/mbc.e05-02-0093] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Arp1p is the only actin-related protein (ARP) known to form actin-like filaments. Unlike actin, Arp1p functions with microtubules, as part of the dynein regulator, dynactin. Arp1p's dissimilar functions imply interactions with a distinct set of proteins. To distinguish surface features relating to Arp1p's core functions and to identify the footprint of protein interactions essential for dynactin function, we performed the first complete charge-cluster-to-alanine scanning mutagenesis of an ARP and compared the results with a similar study of actin. The Arp1p mutations revealed three nonoverlapping surfaces with distinct genetic properties. One of these surfaces encompassed a region unique to Arp1p that is crucial for Jnm1p (dynamitin/p50) and Nip100p (p150(Glued)) association as well as pointed-end associations. Unlike the actin mutations, none of the ARP1 alleles disrupt filament formation; however, one pointed-end allele delayed the elution of Arp1p on gel filtration, consistent with loss of additional subunits.
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Affiliation(s)
- Sean W Clark
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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12
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Rommelaere H, Waterschoot D, Neirynck K, Vandekerckhove J, Ampe C. Structural Plasticity of Functional Actin. Structure 2003; 11:1279-89. [PMID: 14527395 DOI: 10.1016/j.str.2003.09.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Actin is one of the most conserved and versatile proteins capable of forming homopolymers and interacting with numerous other proteins in the cell. We performed an alanine mutagenesis scan covering the entire beta-actin molecule. Somewhat surprisingly, the majority of the mutants were capable of reaching a stable conformation. We tested the ability of these mutants to bind to various actin binding proteins, thereby mapping different interfaces with actin. Additionally, we tested their ability to copolymerize with alpha-actin in order to localize regions in actin that contact neighboring protomers in the filament. Hereby, we could discriminate between two existing models for filamentous actin and our data strongly support the right-handed double-stranded helix model. We present data corroborating this model in vivo. Mutants defective in copolymerization do not colocalize with the actin cytoskeleton and some impair its normal function, thereby disturbing cell shape.
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Affiliation(s)
- Heidi Rommelaere
- Department of Biochemistry and Molecular Biology, Faculty of Medicine and Health Sciences, Ghent University, A. Baertsoenkaai 3, B-9000, Gent, Belgium.
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13
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Sparrow JC, Nowak KJ, Durling HJ, Beggs AH, Wallgren-Pettersson C, Romero N, Nonaka I, Laing NG. Muscle disease caused by mutations in the skeletal muscle alpha-actin gene (ACTA1). Neuromuscul Disord 2003; 13:519-31. [PMID: 12921789 DOI: 10.1016/s0960-8966(03)00101-9] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Mutations in the skeletal muscle alpha-actin gene (ACTA1) associated with congenital myopathy with excess of thin myofilaments, nemaline myopathy and intranuclear rod myopathy were first described in 1999. At that time, only 15 different missense mutations were known in ACTA1. More than 60 mutations have now been identified. This review analyses this larger spectrum of mutations in ACTA1. It investigates the molecular consequences of the mutations found to date, provides a framework for genotype-phenotype correlation and suggests future studies in light of results of investigation of normal and mutant actin in other systems, notably the actin specific to the indirect flight muscles of Drosophila. The larger series confirms that the majority of ACTA1 mutations are dominant, a small number are recessive and most isolated cases with no previous family history have de novo dominant mutations. The severity of the disease caused ranges from lack of spontaneous movements at birth requiring immediate mechanical ventilation, to mild disease compatible with life to adulthood. Overall, the mutations within ACTA1 are randomly distributed throughout the protein. However, the larger series of mutations now available indicates that there may be clustering of mutations associated with some phenotypes, e.g. actin myopathy. This would suggest that interference with certain actin functions may be more associated with certain phenotypes, though the exact pathophysiology of the actin mutations remains unknown.
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Affiliation(s)
- John C Sparrow
- Department of Biology, University of York, York, YO10 5DD, UK
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14
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Eitzen G, Wang L, Thorngren N, Wickner W. Remodeling of organelle-bound actin is required for yeast vacuole fusion. J Cell Biol 2002; 158:669-79. [PMID: 12177043 PMCID: PMC2174018 DOI: 10.1083/jcb.200204089] [Citation(s) in RCA: 139] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Actin participates in several intracellular trafficking pathways. We now find that actin, bound to the surface of purified yeast vacuoles in the absence of cytosol or cytoskeleton, regulates the last compartment mixing stage of homotypic vacuole fusion. The Cdc42p GTPase is known to be required for vacuole fusion. We now show that proteins of the Cdc42p-regulated actin remodeling cascade (Cdc42p --> Cla4p --> Las17p/Vrp1p --> Arp2/3 complex --> actin) are enriched on isolated vacuoles. Vacuole fusion is dramatically altered by perturbation of the vacuole-bound actin, either by mutation of the ACT1 gene, addition of specific actin ligands such as latrunculin B or jasplakinolide, antibody to the actin regulatory proteins Las17p (yeast Wiskott-Aldrich syndrome protein) or Arp2/3, or deletion of actin regulatory genes. On docked vacuoles, actin is enriched at the "vertex ring" membrane microdomain where fusion occurs and is required for the terminal steps leading to membrane fusion. This role for actin may extend to other trafficking systems.
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Affiliation(s)
- Gary Eitzen
- Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755-3844, USA
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15
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Affiliation(s)
- Bruce L Goode
- Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA
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16
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Yin H, You L, Pasqualone D, Kopski KM, Huffaker TC. Stu1p is physically associated with beta-tubulin and is required for structural integrity of the mitotic spindle. Mol Biol Cell 2002; 13:1881-92. [PMID: 12058056 PMCID: PMC117611 DOI: 10.1091/mbc.01-09-0458] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Formation of the bipolar mitotic spindle relies on a balance of forces acting on the spindle poles. The primary outward force is generated by the kinesin-related proteins of the BimC family that cross-link antiparallel interpolar microtubules and slide them past each other. Here, we provide evidence that Stu1p is also required for the production of this outward force in the yeast Saccharomyces cerevisiae. In the temperature-sensitive stu1-5 mutant, spindle pole separation is inhibited, and preanaphase spindles collapse, with their previously separated poles being drawn together. The temperature sensitivity of stu1-5 can be suppressed by doubling the dosage of Cin8p, a yeast BimC kinesin-related protein. Stu1p was observed to be a component of the mitotic spindle localizing to the midregion of anaphase spindles. It also binds to microtubules in vitro, and we have examined the nature of this interaction. We show that Stu1p interacts specifically with beta-tubulin and identify the domains required for this interaction on both Stu1p and beta-tubulin. Taken together, these findings suggest that Stu1p binds to interpolar microtubules of the mitotic spindle and plays an essential role in their ability to provide an outward force on the spindle poles.
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Affiliation(s)
- Hongwei Yin
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA
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17
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Abstract
The yeast a-factor receptor (Ste3p) is subject to two mechanistically distinct modes of endocytosis: a constitutive, ligand-independent pathway links to vacuolar degradation of the receptor, while a ligand-dependent uptake pathway links primarily to recycling and thus, receptor reutilization. Ste3p ubiquitination triggers its uptake into the constitutive pathway. The present work considers the role of the receptor ubiquitination associated with the Ste3p ligand-dependent endocytosis mechanism. The doa4delta mutation which reduces the cellular availability of ubiquitin blocks the Ste3p constitutive uptake. Uptake into the Ste3p ligand-dependent recycling pathway, however, continues unimpaired. The ubiquitin independence of Ste3p ligand-dependent uptake was further indicated by analysis of receptor mutants having Lys-to-Arg substitutions at all possible ubiquitin acceptor sites. Again, the ligand-induced internalization was unimpaired. Furthermore, no discernible effect was seen on either recycling or on the slow PEP4-dependent turnover of the receptor (for receptor internalized via the ligand-dependent mechanism, trafficking to the vacuole/lysosome is the minor, alternate fate to recycling). However, one striking effect of the Lys-to-Arg mutations was noted. Following a prolonged exposure of the cells to the a-factor ligand, rather than being delivered to the vacuolar lumen, the Lys-to-Arg receptor was found to localize instead to the limiting membrane of the vacuole. Thus, while receptor ubiquitination clearly is not required for either the a-factor-dependent uptake into recycling pathway or for the recycling itself, it does affect the routing of receptor to the vacuole, likely by affecting the routing through the late endosomal, multivesicular body: ubiquitinated receptor may be selected into the internal, lumenal vesicles, while unmodified receptor may be left to reside at the limiting external membrane.
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Affiliation(s)
- Linyi Chen
- Department of Physiology, University of Michigan School of Medicine, Ann Arbor, MI 48109, USA
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Bennett V, Baines AJ. Spectrin and ankyrin-based pathways: metazoan inventions for integrating cells into tissues. Physiol Rev 2001; 81:1353-92. [PMID: 11427698 DOI: 10.1152/physrev.2001.81.3.1353] [Citation(s) in RCA: 718] [Impact Index Per Article: 31.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The spectrin-based membrane skeleton of the humble mammalian erythrocyte has provided biologists with a set of interacting proteins with diverse roles in organization and survival of cells in metazoan organisms. This review deals with the molecular physiology of spectrin, ankyrin, which links spectrin to the anion exchanger, and two spectrin-associated proteins that promote spectrin interactions with actin: adducin and protein 4.1. The lack of essential functions for these proteins in generic cells grown in culture and the absence of their genes in the yeast genome have, until recently, limited advances in understanding their roles outside of erythrocytes. However, completion of the genomes of simple metazoans and application of homologous recombination in mice now are providing the first glimpses of the full scope of physiological roles for spectrin, ankyrin, and their associated proteins. These functions now include targeting of ion channels and cell adhesion molecules to specialized compartments within the plasma membrane and endoplasmic reticulum of striated muscle and the nervous system, mechanical stabilization at the tissue level based on transcellular protein assemblies, participation in epithelial morphogenesis, and orientation of mitotic spindles in asymmetric cell divisions. These studies, in addition to stretching the erythrocyte paradigm beyond recognition, also are revealing novel cellular pathways essential for metazoan life. Examples are ankyrin-dependent targeting of proteins to excitable membrane domains in the plasma membrane and the Ca(2+) homeostasis compartment of the endoplasmic reticulum. Exciting questions for the future relate to the molecular basis for these pathways and their roles in a clinical context, either as the basis for disease or more positively as therapeutic targets.
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Affiliation(s)
- V Bennett
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.
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19
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Volkmann N, DeRosier D, Matsudaira P, Hanein D. An atomic model of actin filaments cross-linked by fimbrin and its implications for bundle assembly and function. J Cell Biol 2001; 153:947-56. [PMID: 11381081 PMCID: PMC2174342 DOI: 10.1083/jcb.153.5.947] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2000] [Accepted: 04/13/2001] [Indexed: 11/23/2022] Open
Abstract
Actin bundles have profound effects on cellular shape, division, adhesion, motility, and signaling. Fimbrin belongs to a large family of actin-bundling proteins and is involved in the formation of tightly ordered cross-linked bundles in the brush border microvilli and in the stereocilia of inner ear hair cells. Polymorphism in these three-dimensional (3D) bundles has prevented the detailed structural characterization required for in-depth understanding of their morphogenesis and function. Here, we describe the structural characterization of two-dimensional arrays of actin cross-linked with human T-fimbrin. Structural information obtained by electron microscopy, x-ray crystallography, and homology modeling allowed us to build the first molecular model for the complete actin-fimbrin cross-link. The restriction of the arrays to two dimensions allowed us to deduce the spatial relationship between the components, the mode of fimbrin cross-linking, and the flexibility within the cross-link. The atomic model of the fimbrin cross-link, the cross-linking rules deduced from the arrays, and the hexagonal packing of actin bundles in situ were all combined to generate an atomic model for 3D actin-fimbrin bundles. Furthermore, the assembly of the actin-fimbrin arrays suggests coupling between actin polymerization, fimbrin binding, and crossbridge formation, presumably achieved by a feedback between conformational changes and changes in affinity.
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Affiliation(s)
| | - David DeRosier
- The Rosenstiel Basic Medical Sciences Research Center and The W.M. Keck Institute for Cellular Visualization, Brandeis University, Waltham, Massachusetts 02254
| | - Paul Matsudaira
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142
| | - Dorit Hanein
- The Burnham Institute, La Jolla, California 92037
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20
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Belmont LD, Drubin DG. Actin structure function relationships revealed by yeast molecular genetics. Results Probl Cell Differ 2001; 32:103-21. [PMID: 11131826 DOI: 10.1007/978-3-540-46560-7_8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Affiliation(s)
- L D Belmont
- Department of Molecular and Cell Biology, 401 Barker Hall, University of California, Berkeley, California 94720-3202, USA
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21
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Whitacre J, Davis D, Toenjes K, Brower S, Adams A. Generation of an isogenic collection of yeast actin mutants and identification of three interrelated phenotypes. Genetics 2001; 157:533-43. [PMID: 11156976 PMCID: PMC1461522 DOI: 10.1093/genetics/157.2.533] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A large collection of yeast actin mutations has been previously isolated and used in numerous studies of actin cytoskeletal function. However, the various mutations have been in congenic, rather than isogenic, backgrounds, making it difficult to compare the subtle phenotypes that are characteristic of these mutants. We have therefore placed 27 mutations in an isogenic background. We used a subset of these mutants to compare the degree to which different actin alleles are defective in sporulation, endocytosis, and growth on NaCl-containing media. We found that the three phenotypes are highly correlated. The correlations are specific and not merely a reflection of general growth defects, because the phenotypes are not correlated with growth rates under normal conditions. Significantly, those actin mutants exhibiting the most severe phenotypes in all three processes have altered residues that cluster to a small region of the actin crystal structure previously defined as the fimbrin (Sac6p)-binding site. We examined the relationship between endocytosis and growth on salt and found that shifting wild-type or actin mutant cells to high salt reduces the rate of alpha-factor internalization. These results suggest that actin mutants may be unable to grow on salt because of additive endocytic defects (due to mutation and salt).
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Affiliation(s)
- J Whitacre
- Department of Molecular & Cellular Biology, University of Arizona, Tucson, AZ 85721, USA.
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22
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Asleson CM, Bensen ES, Gale CA, Melms AS, Kurischko C, Berman J. Candida albicans INT1-induced filamentation in Saccharomyces cerevisiae depends on Sla2p. Mol Cell Biol 2001; 21:1272-84. [PMID: 11158313 PMCID: PMC99580 DOI: 10.1128/mcb.21.4.1272-1284.2001] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Candida albicans INT1 gene is important for hyphal morphogenesis, adherence, and virulence (C. Gale, C. Bendel, M. McClellan, M. Hauser, J. M. Becker, J. Berman, and M. Hostetter, Science 279:1355-1358, 1998). The ability to switch between yeast and hyphal morphologies is an important virulence factor in this fungal pathogen. When INT1 is expressed in Saccharomyces cerevisiae, cells grow with a filamentous morphology that we exploited to gain insights into how C. albicans regulates hyphal growth. In S. cerevisiae, INT1-induced filamentous growth was affected by a small subset of actin mutations and a limited set of actin-interacting proteins including Sla2p, an S. cerevisiae protein with similarity in its C terminus to mouse talin. Interestingly, while SLA2 was required for INT1-induced filamentous growth, it was not required for polarized growth in response to several other conditions, suggesting that Sla2p is not required for polarized growth per se. The morphogenesis checkpoint, mediated by Swe1p, contributes to INT1-induced filamentous growth; however, epistasis analysis suggests that Sla2p and Swe1p contribute to INT1-induced filamentous growth through independent pathways. The C. albicans SLA2 homolog (CaSLA2) complements S. cerevisiae sla2Delta mutants for growth at 37 degrees C and INT1-induced filamentous growth. Furthermore, in a C. albicans Casla2/Casla2 strain, hyphal growth did not occur in response to either nutrient deprivation or to potent stimuli, such as mammalian serum. Thus, through analysis of INT1-induced filamentous growth in S. cerevisiae, we have identified a C. albicans gene, SLA2, that is required for hyphal growth in C. albicans.
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Affiliation(s)
- C M Asleson
- Department of Genetics, Cell Biology, and Development, University of Minnesota, St. Paul, Minnesota 55108, USA
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23
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Schaerer-Brodbeck C, Riezman H. Interdependence of filamentous actin and microtubules for asymmetric cell division. Biol Chem 2000; 381:815-25. [PMID: 11076014 DOI: 10.1515/bc.2000.104] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Asymmetric cell divisions are crucial to the generation of cell fate diversity. They contribute to unequal distribution of cellular factors to the daughter cells. Asymmetric divisions are characterized by a 90 degrees rotation of the mitotic spindle. There is increasing evidence that a tight cooperation between cortical, filamentous actin and astral microtubules is indispensable for successful spindle rotation. Over the past years, the dynactin complex has emerged as a key candidate to mediate actin/microtubule interaction at the cortex. This review discusses our current understanding of how spindle rotation is accomplished by the interplay of filamentous actin and microtubules in a variety of experimental systems.
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24
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Tang HY, Xu J, Cai M. Pan1p, End3p, and S1a1p, three yeast proteins required for normal cortical actin cytoskeleton organization, associate with each other and play essential roles in cell wall morphogenesis. Mol Cell Biol 2000; 20:12-25. [PMID: 10594004 PMCID: PMC85029 DOI: 10.1128/mcb.20.1.12-25.2000] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/1999] [Accepted: 09/28/1999] [Indexed: 11/20/2022] Open
Abstract
The EH domain proteins Pan1p and End3p of budding yeast have been known to form a complex in vivo and play important roles in organization of the actin cytoskeleton and endocytosis. In this report, we describe new findings concerning the function of the Pan1p-End3p complex. First, we found that the Pan1p-End3p complex associates with Sla1p, another protein known to be required for the assembly of cortical actin structures. Sla1p interacts with the first long repeat region of Pan1p and the N-terminal EH domain of End3p, thus leaving the Pan1p-End3p interaction, which requires the second long repeat of Pan1p and the C-terminal repeat region of End3p, undisturbed. Second, Pan1p, End3p, and Sla1p are also required for normal cell wall morphogenesis. Each of the Pan1-4, sla1Delta, and end3Delta mutants displays the abnormal cell wall morphology previously reported for the act1-1 mutant. These cell wall defects are also exhibited by wild-type cells overproducing the C-terminal region of Sla1p that is responsible for interactions with Pan1p and End3p. These results indicate that the functions of Pan1p, End3p, and Sla1p in cell wall morphogenesis may depend on the formation of a heterotrimeric complex. Interestingly, the cell wall abnormalities exhibited by these cells are independent of the actin cytoskeleton organization on the cell cortex, as they manifest despite the presence of apparently normal cortical actin cytoskeleton. Examination of several act1 mutants also supports this conclusion. These observations suggest that the Pan1p-End3p-Sla1p complex is required not only for normal actin cytoskeleton organization but also for normal cell wall morphogenesis in yeast.
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Affiliation(s)
- H Y Tang
- Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117609, Singapore
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25
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Keep NH, Winder SJ, Moores CA, Walke S, Norwood FL, Kendrick-Jones J. Crystal structure of the actin-binding region of utrophin reveals a head-to-tail dimer. Structure 1999; 7:1539-46. [PMID: 10647184 DOI: 10.1016/s0969-2126(00)88344-6] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
BACKGROUND Utrophin is a large multidomain protein that belongs to a superfamily of actin-binding proteins, which includes dystrophin, alpha-actinin, beta-spectrin, fimbrin, filamin and plectin. All the members of this family contain a common actin-binding region at their N termini and perform a wide variety of roles associated with the actin cytoskeleton. Utrophin is the autosomal homologue of dystrophin, the protein defective in the X-linked Duchenne and Becker muscular dystrophies, and upregulation of utrophin has been suggested as a potential therapy for muscular dystrophy patients. RESULTS The structure of the actin-binding region of utrophin, consisting of two calponin-homology (CH) domains, has been solved at 3.0 A resolution. It is composed of an antiparallel dimer with each of the monomers being present in an extended dumbell shape and the two CH domains being separated by a long central helix. This extended conformation is in sharp contrast to the compact monomer structure of the N-terminal actin-binding region of fimbrin. CONCLUSIONS The crystal structure of the actin-binding region of utrophin suggests that these actin-binding domains may be more flexible than was previously thought and that this flexibility may allow domain reorganisation and play a role in the actin-binding mechanism. Thus utrophin could possibly bind to actin in an extended conformation so that the sites previously identified as being important for actin binding may be directly involved in this interaction.
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Affiliation(s)
- N H Keep
- MRC Laboratory of Molecular Biology, Cambridge, UK.
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26
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Rodal AA, Tetreault JW, Lappalainen P, Drubin DG, Amberg DC. Aip1p interacts with cofilin to disassemble actin filaments. J Cell Biol 1999; 145:1251-64. [PMID: 10366597 PMCID: PMC2133144 DOI: 10.1083/jcb.145.6.1251] [Citation(s) in RCA: 178] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/1998] [Revised: 05/05/1999] [Indexed: 11/22/2022] Open
Abstract
Actin interacting protein 1 (Aip1) is a conserved component of the actin cytoskeleton first identified in a two-hybrid screen against yeast actin. Here, we report that Aip1p also interacts with the ubiquitous actin depolymerizing factor cofilin. A two-hybrid-based approach using cofilin and actin mutants identified residues necessary for the interaction of actin, cofilin, and Aip1p in an apparent ternary complex. Deletion of the AIP1 gene is lethal in combination with cofilin mutants or act1-159, an actin mutation that slows the rate of actin filament disassembly in vivo. Aip1p localizes to cortical actin patches in yeast cells, and this localization is disrupted by specific actin and cofilin mutations. Further, Aip1p is required to restrict cofilin localization to cortical patches. Finally, biochemical analyses show that Aip1p causes net depolymerization of actin filaments only in the presence of cofilin and that cofilin enhances binding of Aip1p to actin filaments. We conclude that Aip1p is a cofilin-associated protein that enhances the filament disassembly activity of cofilin and restricts cofilin localization to cortical actin patches.
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Affiliation(s)
- A A Rodal
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720, USA
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27
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Belmont LD, Patterson GM, Drubin DG. New actin mutants allow further characterization of the nucleotide binding cleft and drug binding sites. J Cell Sci 1999; 112 ( Pt 9):1325-36. [PMID: 10194411 DOI: 10.1242/jcs.112.9.1325] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have generated 9 site-specific mutations in Saccharomyces cerevisiae actin. These mutants display a variety of phenotypes when expressed in vivo, including slow actin filament turnover, slow fluid-phase endocytosis, and defects in actin organization. Actin mutation D157E confers resistance to the actin-sequestering drug, latrunculin A. Latrunculin A inhibits nucleotide exchange on wild-type yeast actin but not on D157E actin, suggesting that this residue is part of the latrunculin A binding site. We have refined our earlier map of the phalloidin binding site on actin, demonstrating a requirement for residue G158 in addition to D179 and R177. The nine new actin mutants as well as a large collection of existing actin mutants were also used to identify the putative binding site of another actin binding drug, tolytoxin, on actin. The actin alleles that result in decreased sensitivity to this drug cluster at a site near the nucleotide-binding pocket. Actin purified from one of these mutants has a reduced affinity for tolytoxin. In addition, tolytoxin causes a 2.4-fold increase in the t1/2 of ATP exchange, further suggesting that this drug binds near the nucleotide-binding pocket of actin. We note that the binding sites for latrunculin A, phalloidin, and tolytoxin all map close to the actin nucleotide binding pocket.
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Affiliation(s)
- L D Belmont
- Department of Molecular and Cell Biology, University of California, Berkeley CA 94720-3202, USA
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28
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Abstract
A major mechanism of mRNA decay in yeast is initiated by deadenylation, followed by mRNA decapping, which exposes the transcript to 5' to 3' exonucleolytic degradation. The decapping enzyme that removes the 5' cap structure is encoded by the DCP1 gene. To understand the function of the decapping enzyme, we used alanine scanning mutagenesis to create 31 mutant versions of the enzyme, and we examined the effects of the mutations both in vivo and in vitro. Two types of mutations that affected mRNA decapping in vivo were identified, including a temperature-sensitive allele. First, two mutants produced decapping enzymes that were defective for decapping in vitro, suggesting that these mutated residues are required for enzymatic activity. In contrast, several mutants that moderately affected mRNA decapping in vivo yielded decapping enzymes that had at least the same specific activity as the wild-type enzyme in vitro. Combination of alleles within this group yielded decapping enzymes that showed a strong loss of function in vivo, but that still produced fully active enzymes in vitro. This suggested that interactions of the decapping enzyme with other factors may be required for efficient decapping in vivo, and that these particular mutations may be disrupting such interactions. Interestingly, partial loss of decapping activity in vivo led to a defect in normal deadenylation-dependent decapping, but it did not affect the rapid deadenylation-independent decapping triggered by early nonsense codons. This observation suggested that these two types of mRNA decapping differ in their requirements for the decapping enzyme.
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Affiliation(s)
- S Tharun
- Departments of Molecular and Cellular Biology and Biochemistry and the Howard Hughes Medical Institute, University of Arizona, Tucson, Arizona 85721-0106, USA
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29
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Blader IJ, Cope MJ, Jackson TR, Profit AA, Greenwood AF, Drubin DG, Prestwich GD, Theibert AB. GCS1, an Arf guanosine triphosphatase-activating protein in Saccharomyces cerevisiae, is required for normal actin cytoskeletal organization in vivo and stimulates actin polymerization in vitro. Mol Biol Cell 1999; 10:581-96. [PMID: 10069805 PMCID: PMC25189 DOI: 10.1091/mbc.10.3.581] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Recent cloning of a rat brain phosphatidylinositol 3,4, 5-trisphosphate binding protein, centaurin alpha, identified a novel gene family based on homology to an amino-terminal zinc-binding domain. In Saccharomyces cerevisiae, the protein with the highest homology to centaurin alpha is Gcs1p, the product of the GCS1 gene. GCS1 was originally identified as a gene conditionally required for the reentry of cells into the cell cycle after stationary phase growth. Gcs1p was previously characterized as a guanosine triphosphatase-activating protein for the small guanosine triphosphatase Arf1, and gcs1 mutants displayed vesicle-trafficking defects. Here, we have shown that similar to centaurin alpha, recombinant Gcs1p bound phosphoinositide-based affinity resins with high affinity and specificity. A novel GCS1 disruption strain (gcs1Delta) exhibited morphological defects, as well as mislocalization of cortical actin patches. gcs1Delta was hypersensitive to the actin monomer-sequestering drug, latrunculin-B. Synthetic lethality was observed between null alleles of GCS1 and SLA2, the gene encoding a protein involved in stabilization of the actin cytoskeleton. In addition, synthetic growth defects were observed between null alleles of GCS1 and SAC6, the gene encoding the yeast fimbrin homologue. Recombinant Gcs1p bound to actin filaments, stimulated actin polymerization, and inhibited actin depolymerization in vitro. These data provide in vivo and in vitro evidence that Gcs1p interacts directly with the actin cytoskeleton in S. cerevisiae.
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Affiliation(s)
- I J Blader
- Departments of Neurobiology and Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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30
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Shannon KB, Li R. The multiple roles of Cyk1p in the assembly and function of the actomyosin ring in budding yeast. Mol Biol Cell 1999; 10:283-96. [PMID: 9950677 PMCID: PMC25169 DOI: 10.1091/mbc.10.2.283] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The budding yeast IQGAP-like protein Cyk1p/Iqg1p localizes to the mother-bud junction during anaphase and has been shown to be required for the completion of cytokinesis. In this study, video microscopy analysis of cells expressing green fluorescent protein-tagged Cyk1p/Iqg1p demonstrates that Cyk1p/Iqg1p is a dynamic component of the contractile ring during cytokinesis. Furthermore, in the absence of Cyk1p/Iqg1p, myosin II fails to undergo the contraction-like size change at the end of mitosis. To understand the mechanistic role of Cyk1p/Iqg1p in actomyosin ring assembly and dynamics, we have investigated the role of the structural domains that Cyk1p/Iqg1p shares with IQGAPs. An amino terminal portion containing the calponin homology domain binds to actin filaments and is required for the assembly of actin filaments to the ring. This result supports the hypothesis that Cyk1p/Iqg1p plays a direct role in F-actin recruitment. Deletion of the domain harboring the eight IQ motifs abolishes the localization of Cyk1p/Iqg1p to the bud neck, suggesting that Cyk1p/Iqg1p may be localized through interactions with a calmodulin-like protein. Interestingly, deletion of the COOH-terminal GTPase-activating protein-related domain does not affect Cyk1p/Iqg1p localization or actin recruitment to the ring but prevents actomyosin ring contraction. In vitro binding experiments show that Cyk1p/Iqg1p binds to calmodulin, Cmd1p, in a calcium-dependent manner, and to Tem1p, a small GTP-binding protein previously found to be required for the completion of anaphase. These results demonstrate the critical function of Cyk1p/Iqg1p in regulating various steps of actomyosin ring assembly and cytokinesis.
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Affiliation(s)
- K B Shannon
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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31
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Zeng G, Cai M. Regulation of the actin cytoskeleton organization in yeast by a novel serine/threonine kinase Prk1p. J Cell Biol 1999; 144:71-82. [PMID: 9885245 PMCID: PMC2148122 DOI: 10.1083/jcb.144.1.71] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Normal actin cytoskeleton organization in budding yeast requires the function of the Pan1p/ End3p complex. Mutations in PAN1 and END3 cause defects in the organization of actin cytoskeleton and endocytosis. By screening for mutations that can suppress the temperature sensitivity of a pan1 mutant (pan1-4), a novel serine/threonine kinase Prk1p is now identified as a new factor regulating the actin cytoskeleton organization in yeast. The suppression of pan1-4 by prk1 requires the presence of mutant Pan1p. Although viable, the prk1 mutant is unable to maintain an asymmetric distribution of the actin cytoskeleton at 37 degreesC. Consistent with its role in the regulation of actin cytoskeleton, Prk1p localizes to the regions of cell growth and coincides with the polarized actin patches. Overexpression of the PRK1 gene in wild-type cells leads to lethality and actin cytoskeleton abnormalities similar to those exhibited by the pan1 and end3 mutants. In vitro phosphorylation assays demonstrate that Prk1p is able to phosphorylate regions of Pan1p containing the LxxQxTG repeats, including the region responsible for binding to End3p. Based on these findings, we propose that the Prk1 protein kinase regulates the actin cytoskeleton organization by modulating the activities of some actin cytoskeleton-related proteins such as Pan1p/End3p.
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Affiliation(s)
- G Zeng
- Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117609
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32
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Feierbach B, Nogales E, Downing KH, Stearns T. Alf1p, a CLIP-170 domain-containing protein, is functionally and physically associated with alpha-tubulin. J Cell Biol 1999; 144:113-24. [PMID: 9885248 PMCID: PMC2148126 DOI: 10.1083/jcb.144.1.113] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/1998] [Revised: 12/07/1998] [Indexed: 11/25/2022] Open
Abstract
Tubulin is a heterodimer of alpha- and beta-tubulin polypeptides. Assembly of the tubulin heterodimer in vitro requires the CCT chaperonin complex, and a set of five proteins referred to as the tubulin cofactors (Tian, F., Y. Huang, H. Rommelaere, J. Vandekerckhove, C. Ampe, and N.J. Cowan. 1996. Cell. 86:287-296; Tian, G., S.A. Lewis, B. Feierbach, T. Stearns, H. Rommelaere, C. Ampe, and N.J. Cowan. 1997. J. Cell Biol. 138:821-832). We report the characterization of Alf1p, the yeast ortholog of mammalian cofactor B. Alf1p interacts with alpha-tubulin in both two-hybrid and immunoprecipitation assays. Alf1p and cofactor B contain a single CLIP-170 domain, which is found in several microtubule-associated proteins. Mutation of the CLIP-170 domain in Alf1p disrupts the interaction with alpha-tubulin. Mutations in alpha-tubulin that disrupt the interaction with Alf1p map to a domain on the cytoplasmic face of alpha-tubulin; this domain is distinct from the region of interaction between alpha-tubulin and beta-tubulin. Alf1p-green fluorescent protein (GFP) is able to associate with microtubules in vivo, and this localization is abolished either by mutation of the CLIP-170 domain in Alf1p, or by mutation of the Alf1p-binding domain in alpha-tubulin. Analysis of double mutants constructed between null alleles of ALF1 and PAC2, which encodes the other yeast alpha-tubulin cofactor, suggests that Alf1p and Pac2p act in the same pathway leading to functional alpha-tubulin. The phenotype of overexpression of ALF1 suggests that Alf1p can act to sequester alpha-tubulin from interaction with beta-tubulin, raising the possibility that it plays a regulatory role in the formation of the tubulin heterodimer.
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Affiliation(s)
- B Feierbach
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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33
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Hanein D, Volkmann N, Goldsmith S, Michon AM, Lehman W, Craig R, DeRosier D, Almo S, Matsudaira P. An atomic model of fimbrin binding to F-actin and its implications for filament crosslinking and regulation. NATURE STRUCTURAL BIOLOGY 1998; 5:787-92. [PMID: 9731773 DOI: 10.1038/1828] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Using a new procedure that combines electron-density correlation with biochemical information, we have fitted the crystal structure of the N-terminal actin-binding domain of human T-fimbrin to helical reconstructions of fimbrin-decorated actin filaments. The map locates the N-terminal calcium-binding domain and identifies actin-binding site residues on the two calponin-homology domains of fimbrin. Based on this map, we propose a model of a fimbrin crosslink in an actin bundle and its regulation by calcium.
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Affiliation(s)
- D Hanein
- The W.M. Keck Institute for Cellular Visualization, Brandeis University, Waltham, Massachusetts 02254, USA.
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Cali BM, Doyle TC, Botstein D, Fink GR. Multiple functions for actin during filamentous growth of Saccharomyces cerevisiae. Mol Biol Cell 1998; 9:1873-89. [PMID: 9658177 PMCID: PMC25429 DOI: 10.1091/mbc.9.7.1873] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/1998] [Accepted: 03/13/1998] [Indexed: 11/11/2022] Open
Abstract
Saccharomyces cerevisiae is dimorphic and switches from a yeast form to a pseudohyphal (PH) form when starved for nitrogen. PH cells are elongated, bud in a unipolar manner, and invade the agar substrate. We assessed the requirements for actin in mediating the dramatic morphogenetic events that accompany the transition to PH growth. Twelve "alanine scan" alleles of the single yeast actin gene (ACT1) were tested for effects on filamentation, unipolar budding, agar invasion, and cell elongation. Some act1 mutations affect all phenotypes, whereas others affect only one or two aspects of PH growth. Tests of intragenic complementation among specific act1 mutations support the phenotypic evidence for multiple actin functions in filamentous growth. We present evidence that interaction between actin and the actin-binding protein fimbrin is important for PH growth and suggest that association of different actin-binding proteins with actin mediates the multiple functions of actin in filamentous growth. Furthermore, characterization of cytoskeletal structure in wild type and act1/act1 mutants indicates that PH cell morphogenesis requires the maintenance of a highly polarized actin cytoskeleton. Collectively, this work demonstrates that actin plays a central role in fungal dimorphism.
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Affiliation(s)
- B M Cali
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
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35
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Sandrock TM, O'Dell JL, Adams AE. Allele-specific suppression by formation of new protein-protein interactions in yeast. Genetics 1997; 147:1635-42. [PMID: 9409826 PMCID: PMC1208336 DOI: 10.1093/genetics/147.4.1635] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Yeast fimbrin is encoded by the SAC6 gene, mutations of which suppress temperature-sensitive mutations in the actin gene (ACT1). To examine the mechanism of suppression, we have conducted a biochemical analysis of the interaction between various combinations of wild-type and mutant actin and Sac6 proteins. Previously, we showed that actin mutations that are suppressed by sac6 mutations encode proteins with a reduced affinity for wild-type Sac6p. In the present study, we have found that mutant Sac6 proteins bind more tightly to mutant actin than does wild-type Sac6p, and thus compensate for weakened interactions caused by the mutant actin. Remarkably, we have also found that mutant Sac6 proteins bind more tightly to wild-type actin than does wild-type Sac6p. This result indicates that suppression does not occur through the restoration of the original contact site, but rather through the formation of a novel contact site. This finding argues against suppression occurring through a "lock-and-key" mechanism and suggests a mechanism involving more global increases in affinity between the two proteins. We propose that the most common kind of suppressors involving interacting proteins will likely occur through this less specific mechanism.
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Affiliation(s)
- T M Sandrock
- Department of Molecular and Cellular Biology, Life Sciences South, University of Arizona, Tucson 85721, USA
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Schwartz K, Richards K, Botstein D. BIM1 encodes a microtubule-binding protein in yeast. Mol Biol Cell 1997; 8:2677-91. [PMID: 9398684 PMCID: PMC25736 DOI: 10.1091/mbc.8.12.2677] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/1997] [Accepted: 09/15/1997] [Indexed: 02/05/2023] Open
Abstract
A previously uncharacterized yeast gene (YER016w) that we have named BIM1 (binding to microtubules) was obtained from a two-hybrid screen of a yeast cDNA library using as bait the entire coding sequence of TUB1 (encoding alpha-tubulin). Deletion of BIM1 results in a strong bilateral karyogamy defect, hypersensitivity to benomyl, and aberrant spindle behavior, all phenotypes associated with mutations affecting microtubules in yeast, and inviability at extreme temperatures (i.e., >/=37 degrees C or =14 degrees C). Overexpression of BIM1 in wild-type cells is lethal. A fusion of Bim1p with green fluorescent protein that complements the bim1Delta phenotypes allows visualization in vivo of both intranuclear spindles and extranuclear microtubules in otherwise wild-type cells. A bim1 deletion displays synthetic lethality with deletion alleles of bik1, num1, and bub3 as well as a limited subset of tub1 conditional-lethal alleles. A systematic study of 51 tub1 alleles suggests a correlation between specific failure to interact with Bim1p in the two-hybrid assay and synthetic lethality with the bim1Delta allele. The sequence of BIM1 shows substantial similarity to sequences from organisms across the evolutionary spectrum. One of the human homologues, EB1, has been reported previously as binding APC, itself a microtubule-binding protein and the product of a gene implicated in the etiology of human colon cancer.
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Affiliation(s)
- K Schwartz
- Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA
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37
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Hanein D, Matsudaira P, DeRosier DJ. Evidence for a conformational change in actin induced by fimbrin (N375) binding. J Cell Biol 1997; 139:387-96. [PMID: 9334343 PMCID: PMC2139807 DOI: 10.1083/jcb.139.2.387] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/1996] [Revised: 08/06/1997] [Indexed: 02/05/2023] Open
Abstract
Fimbrin belongs to a superfamily of actin cross-linking proteins that share a conserved 27-kD actin-binding domain. This domain contains a tandem duplication of a sequence that is homologous to calponin. Calponin homology (CH) domains not only cross-link actin filaments into bundles and networks, but they also bind intermediate filaments and some signal transduction proteins to the actin cytoskeleton. This fundamental role of CH domains as a widely used actin-binding domain underlines the necessity to understand their structural interaction with actin. Using electron cryomicroscopy, we have determined the three-dimensional structure of F-actin and F-actin decorated with the NH2-terminal CH domains of fimbrin (N375). In a difference map between actin filaments and N375-decorated actin, one end of N375 is bound to a concave surface formed between actin subdomains 1 and 2 on two neighboring actin monomers. In addition, a fit of the atomic model for the actin filament to the maps reveals the actin residues that line, the binding surface. The binding of N375 changes actin, which we interpret as a movement of subdomain 1 away from the bound N375. This change in actin structure may affect its affinity for other actin-binding proteins and may be part of the regulation of the cytoskeleton itself. Difference maps between actin and actin decorated with other proteins provides a way to look for novel structural changes in actin.
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Affiliation(s)
- D Hanein
- The W.M. Keck Institute for Cellular Visualization and The Rosenstiel Basic Medical Sciences Research Center, Department of Biology, Brandeis University, Waltham, Massachusetts 02254, USA
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38
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Goldsmith SC, Pokala N, Matsudaira P, Almo SC. Crystallization and preliminary crystallographic analysis of the N-terminal actin binding domain of human fimbrin. Proteins 1997; 28:452-3. [PMID: 9223189 DOI: 10.1002/(sici)1097-0134(199707)28:3<452::aid-prot13>3.0.co;2-g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We have crystallized the N-terminal actin binding domain (ABD1) of human fimbrin, a representative member of the largest class of actin crosslinking proteins. Diffraction from these crystals is consistent with the orthorhombic space group P2(1)2(1)2(1) (a = 50.03 A, b = 61.24 A, c = 102.30 A). These crystals contain one molecule in the asymmetric unit and diffract to at least 1.9 A resolution. The crystal structure of ABD1 will be the first structure of an actin crosslinking domain.
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Affiliation(s)
- S C Goldsmith
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Moreau V, Galan JM, Devilliers G, Haguenauer-Tsapis R, Winsor B. The yeast actin-related protein Arp2p is required for the internalization step of endocytosis. Mol Biol Cell 1997; 8:1361-75. [PMID: 9243513 PMCID: PMC276158 DOI: 10.1091/mbc.8.7.1361] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Saccharomyces cerevisiae actin-related protein Arp2p is an essential component of the actin cytoskeleton. We have tested its potential role in the endocytic and exocytic pathways by using a temperature-sensitive allele, arp2-1. The fate of the plasma membrane transporter uracil permease was followed to determine whether Arp2p plays a role in the endocytic pathway. Inhibition of normal endocytosis as revealed by maintenance of active uracil permease at the plasma membrane and strong protection against subsequent vacuolar degradation of the protein were observed in the mutant at the restrictive temperature. Furthermore, arp2-1 cells accumulated ubiquitin-permease conjugates, formed prior to internalization. These effects were also visible at permissive temperature, whereas the actin cytoskeleton appeared to be normally polarized. The soluble hydrolase carboxypeptidase Y and the lipophilic dye FM 4-64 were targeted normally to the vacuole in arp2-1 cells. Thus, Arp2p is required for internalization but does not play a major role in later steps of endocytosis. Synthetic lethality was demonstrated between arp2-1 and the endocytic mutant end3-1, suggesting participation of Arp2p and End3p in the same process. Finally, no evidence for a major defect in secretion was apparent; invertase secretion and delivery of uracil permease to the plasma membrane were unaffected in arp2-1 cells.
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Affiliation(s)
- V Moreau
- Institut de Biologie Moléculaire et Cellulaire-Centre National de la Scientifique, Strasbourg, France
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41
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Ayscough KR, Stryker J, Pokala N, Sanders M, Crews P, Drubin DG. High rates of actin filament turnover in budding yeast and roles for actin in establishment and maintenance of cell polarity revealed using the actin inhibitor latrunculin-A. J Cell Biol 1997; 137:399-416. [PMID: 9128251 PMCID: PMC2139767 DOI: 10.1083/jcb.137.2.399] [Citation(s) in RCA: 611] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We report that the actin assembly inhibitor latrunculin-A (LAT-A) causes complete disruption of the yeast actin cytoskeleton within 2-5 min, suggesting that although yeast are nonmotile, their actin filaments undergo rapid cycles of assembly and disassembly in vivo. Differences in the LAT-A sensitivities of strains carrying mutations in components of the actin cytoskeleton suggest that tropomyosin, fimbrin, capping protein, Sla2p, and Srv2p act to increase actin cytoskeleton stability, while End3p and Sla1p act to decrease stability. Identification of three LAT-A resistant actin mutants demonstrated that in vivo effects of LAT-A are due specifically to impairment of actin function and implicated a region on the three-dimensional actin structure as the LAT-A binding site. LAT-A was used to determine which of 19 different proteins implicated in cell polarity development require actin to achieve polarized localization. Results show that at least two molecular pathways, one actin-dependent and the other actin-independent, underlie polarity development. The actin-dependent pathway localizes secretory vesicles and a putative vesicle docking complex to sites of cell surface growth, providing an explanation for the dependence of polarized cell surface growth on actin function. Unexpectedly, several proteins that function with actin during cell polarity development, including an unconventional myosin (Myo2p), calmodulin, and an actin-interacting protein (Bud6/Aip3p), achieved polarized localization by an actin-independent pathway, revealing interdependence among cell polarity pathways. Finally, transient actin depolymerization caused many cells to abandon one bud site or mating projection and to initiate growth at a second site. Thus, actin filaments are also required for maintenance of an axis of cell polarity.
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Affiliation(s)
- K R Ayscough
- Department of Molecular and Cell Biology, University of California, Berkeley 94720-3202, USA
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42
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Amberg DC, Zahner JE, Mulholland JW, Pringle JR, Botstein D. Aip3p/Bud6p, a yeast actin-interacting protein that is involved in morphogenesis and the selection of bipolar budding sites. Mol Biol Cell 1997; 8:729-53. [PMID: 9247651 PMCID: PMC276122 DOI: 10.1091/mbc.8.4.729] [Citation(s) in RCA: 152] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
A search for Saccharomyces cerevisiae proteins that interact with actin in the two-hybrid system and a screen for mutants that affect the bipolar budding pattern identified the same gene, AIP3/BUD6. This gene is not essential for mitotic growth but is necessary for normal morphogenesis. MATa/alpha daughter cells lacking Aip3p place their first buds normally at their distal poles but choose random sites for budding in subsequent cell cycles. This suggests that actin and associated proteins are involved in placing the bipolar positional marker at the division site but not at the distal tip of the daughter cell. In addition, although aip3 mutant cells are not obviously defective in the initial polarization of the cytoskeleton at the time of bud emergence, they appear to lose cytoskeletal polarity as the bud enlarges, resulting in the formation of cells that are larger and rounder than normal. aip3 mutant cells also show inefficient nuclear migration and nuclear division, defects in the organization of the secretory system, and abnormal septation, all defects that presumably reflect the involvement of Aip3p in the organization and/or function of the actin cytoskeleton. The sequence of Aip3p is novel but contains a predicted coiled-coil domain near its C terminus that may mediate the observed homo-oligomerization of the protein. Aip3p shows a distinctive localization pattern that correlates well with its likely sites of action: it appears at the presumptive bud site prior to bud emergence, remains near the tips of small bund, and forms a ring (or pair of rings) in the mother-bud neck that is detectable early in the cell cycle but becomes more prominent prior to cytokinesis. Surprisingly, the localization of Aip3p does not appear to require either polarized actin or the septin proteins of the neck filaments.
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Affiliation(s)
- D C Amberg
- Department of Genetics, Stanford University School of Medicine, California 94305-5120, USA
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43
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Affiliation(s)
- B Winsor
- Institut de Biologie Moléculaire et Cellulaire, UPR 9005 du CNRS, Strasbourg, France
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44
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Prassler J, Stocker S, Marriott G, Heidecker M, Kellermann J, Gerisch G. Interaction of a Dictyostelium member of the plastin/fimbrin family with actin filaments and actin-myosin complexes. Mol Biol Cell 1997; 8:83-95. [PMID: 9017597 PMCID: PMC276061 DOI: 10.1091/mbc.8.1.83] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
A protein purified from cytoskeletal fractions of Dictyostelium discoideum proved to be a member of the fimbrin/plastin family of actin-bundling proteins. Like other family members, this Ca(2+)-inhibited 67-kDa protein contains two EF hands followed by two actin-binding sites of the alpha-actinin/beta-spectrin type. Dd plastin interacted selectively with actin isoforms: it bound to D. discoideum actin and to beta/gamma-actin from bovine spleen but not to alpha-actin from rabbit skeletal muscle. Immunofluorescence labeling of growth phase cells showed accumulation of Dd plastin in cortical structures associated with cell surface extensions. In the elongated, streaming cells of the early aggregation stage, Dd plastin was enriched in the front regions. To examine how the bundled actin filaments behave in myosin II-driven motility, complexes of F-actin and Dd plastin were bound to immobilized heavy meromyosin, and motility was started by photoactivating caged ATP. Actin filaments were immediately propelled out of bundles or even larger aggregates and moved on the myosin as separate filaments. This result shows that myosin can disperse an actin network when it acts as a motor and sheds light on the dynamics of protein-protein interactions in the cortex of a motile cell where myosin II and Dd plastin are simultaneously present.
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Affiliation(s)
- J Prassler
- Max-Planck-Institut für Biochemie, Martinsried, Germany
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45
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Abstract
Three of the most important questions concerning actin function are: (a) How does actin structure relate to actin function? (b) How does each of the numerous proteins that interact with actin contribute to actin cytoskeleton function in vivo? (c) How are the activities of these proteins regulated? Powerful molecular genetics combined with well-established biochemical techniques make the yeast Saccharomyces cerevisiae an ideal organism for studies aimed at answering these questions. The protein sequences and biochemical properties of actin and its interacting proteins and the pathways that regulate these interactions all appear to be conserved, indicating that principles elucidated from studies in yeast will apply to all eukaryotes. In this review, we highlight advances in our general understanding of actin properties, interactions with other proteins, and regulation of the actin cytoskeleton, derived from studies in the budding yeast S. cerevisiae.
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Affiliation(s)
- K R Ayscough
- Department of Molecular and Cell Biology, University of California, Berkeley 94720-3202, USA
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Höfer D, Drenckhahn D. Cytoskeletal differences between stereocilia of the human sperm passageway and microvilli/stereocilia in other locations. Anat Rec (Hoboken) 1996; 245:57-64. [PMID: 8731041 DOI: 10.1002/(sici)1097-0185(199605)245:1<57::aid-ar10>3.0.co;2-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Stereocilia of the human ductus epididymidis and ductus deferens display unique features in that they arise from an apical cell protrusion (hillock) and contain thick stem portions which are interconnected by cytoplasmic bridges. The molecular basis for this unique fusion and branching pattern is hitherto unknown. These morphologic specialties led us to study the cytoskeleton of male spermway stereocilia with respect to the major proteins that constitute the supportive cytoskeleton of intestinal microvilli and inner ear stereocilia. METHODS Samples of the human epididymidis and ductus deferens were studied by immunoblotting and immunocytochemistry at the light and electron microscope levels. RESULTS Spermway stereocilia are supported by an internal actin filament bundle crosslinked by fimbrin and associated with the membrane linker molecule ezrin. The stem portions and hillock area are supplied with the crossbridge forming molecule alpha-actinin. Spermway stereocilia differ from brush border microvilli of the intestine, kidney, and ductuli efferentes by the lack of the second bundling protein villin and the unusual expression of alpha-actinin in the stem region. They resemble inner ear stereocilia by the presence of fimbrin and absence of villin, but differ from them by expression of ezrin and alpha-actinin. Thus, the main molecular difference between spermway stereocilia and stereocilia/microvilli of other locations is the presence of alpha-actinin in their stem portion and the hillock area. CONCLUSIONS Since alpha-actinin can form crossbridges between adjacent actin filaments (bundles) at longer distances than the other crosslinker of the stereocilium core bundle, fimbrin, we assume that alpha-actinin is essential for both the formation of the stem portions of spermway stereocilia and for the generation of their striking branching pattern. A developmentally regulated temporal sequence of expression of fimbrin and alpha-actinin might control the unique architecture of spermway stereocilia.
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Affiliation(s)
- D Höfer
- Institute of Anatomy, Julius-Maximilians-University Würzburg, Germany
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47
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Doyle T, Botstein D. Movement of yeast cortical actin cytoskeleton visualized in vivo. Proc Natl Acad Sci U S A 1996; 93:3886-91. [PMID: 8632984 PMCID: PMC39454 DOI: 10.1073/pnas.93.9.3886] [Citation(s) in RCA: 231] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Fusion proteins between the green fluorescent protein (GFP) and the cytoskeleton proteins Act1p (actin), Sac6p (yeast fimbrin homolog), and Abp1p in budding yeast (Saccharomyces cerevisiae) localize to the cortical actin patches. The actin fusions could not function as the sole actin source in yeast, but fusions between the actin-binding proteins Abp1p and Sac6p complement fully the phenotypes associated with their gene deletions. Direct observation in vivo reveals that the actin cortical patches move. Movement of actin patches is constrained to the asymmetric distribution of the patches in growing cells, and this movement is greatly reduced when metabolic inhibitors such as sodium azide are added. Fusion protein-labeled patches are normally distributed during the yeast cell cycle and during mating. In vivo observation made possible the visualization of actin patches during sporulation as well.
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Affiliation(s)
- T Doyle
- Department of Genetics, Stanford University Medical Center, CA 94305-5120, USA
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48
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Karpova TS, Tatchell K, Cooper JA. Actin filaments in yeast are unstable in the absence of capping protein or fimbrin. J Cell Biol 1995; 131:1483-93. [PMID: 8522605 PMCID: PMC2120666 DOI: 10.1083/jcb.131.6.1483] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Many actin-binding proteins affect filament assembly in vitro and localize with actin in vivo, but how their molecular actions contribute to filament assembly in vivo is not understood well. We report here that capping protein (CP) and fimbrin are both important for actin filament assembly in vivo in Saccharomyces cerevisiae, based on finding decreased actin filament assembly in CP and fimbrin mutants. We have also identified mutations in actin that enhance the CP phenotype and find that those mutants also have decreased actin filament assembly in vivo. In vitro, actin purified from some of these mutants is defective in polymerization or binding fimbrin. These findings support the conclusion that CP acts to stabilize actin filaments in vivo. This conclusion is particularly remarkable because it is the opposite of the conclusion drawn from recent studies in Dictyostelium (Hug, C., P.Y. Jay, I. Reddy, J.G. McNally, P.C. Bridgman, E.L. Elson, and J.A. Cooper. 1995. Cell. 81:591-600). In addition, we find that the unpolymerized pool of actin in yeast is very small relative to that found in higher cells, which suggests that actin filament assembly is less dynamic in yeast than higher cells.
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Affiliation(s)
- T S Karpova
- Department of Cell Biology and Physiology, Washington University Medical School, St. Louis, Missouri, USA
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Buchberger A, Theyssen H, Schröder H, McCarty JS, Virgallita G, Milkereit P, Reinstein J, Bukau B. Nucleotide-induced conformational changes in the ATPase and substrate binding domains of the DnaK chaperone provide evidence for interdomain communication. J Biol Chem 1995; 270:16903-10. [PMID: 7622507 DOI: 10.1074/jbc.270.28.16903] [Citation(s) in RCA: 198] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Interactions of the DnaK (Hsp70) chaperone from Escherichia coli with substrates are controlled by ATP. Nucleotide-induced changes in DnaK conformation were investigated by monitoring changes in tryptic digestion pattern and tryptophan fluorescence. Using nucleotide-free DnaK preparations, not only the known ATP-induced major changes in kinetics and pattern of proteolysis but also minor ADP-induced changes were detected. Similar ATP-induced conformational changes occurred in the DnaK-T199A mutant protein defective in ATPase activity, demonstrating that they result from binding, not hydrolysis, of ATP. N-terminal sequencing and immunological mapping of tryptic fragments of DnaK identified cleavage sites that, upon ATP addition, appeared within the proposed C-terminal substrate binding region and disappeared in the N-terminal ATPase domain. They hence reflect structural alterations in DnaK correlated to substrate release and indicate ATP-dependent domain interactions. Domain interactions are a prerequisite for efficient tryptic degradation as fragments of DnaK comprising the ATPase and C-terminal domains were highly protease-resistant. Fluorescence analysis of the N-terminally located single tryptophan residue of DnaK revealed that the known ATP-induced alteration of the emission spectrum, proposed to result directly from conformational changes in the ATPase domain, requires the presence of the C-terminal domain and therefore mainly results from altered domain interaction. Analyses of the C-terminally truncated DnaK163 mutant protein revealed that nucleotide-dependent interdomain communication requires a 15-kDa segment assumed to constitute the substrate binding site.
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Affiliation(s)
- A Buchberger
- Zentrum für Molekulare Biologie, Universität Heidelberg, Germany
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50
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Li R, Zheng Y, Drubin DG. Regulation of cortical actin cytoskeleton assembly during polarized cell growth in budding yeast. J Biophys Biochem Cytol 1995; 128:599-615. [PMID: 7860633 PMCID: PMC2199892 DOI: 10.1083/jcb.128.4.599] [Citation(s) in RCA: 130] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have established an in vitro assay for assembly of the cortical actin cytoskeleton of budding yeast cells. After permeabilization of yeast by a novel procedure designed to maintain the spatial organization of cellular constituents, exogenously added fluorescently labeled actin monomers assemble into distinct structures in a pattern that is similar to the cortical actin distribution in vivo. Actin assembly in the bud of small-budded cells requires a nucleation activity provided by protein factors that appear to be distinct from the barbed ends of endogenous actin filaments. This nucleation activity is lost in cells that lack either Sla1 or Sla2, proteins previously implicated in cortical actin cytoskeleton function, suggesting a possible role for these proteins in the nucleation reaction. The rate and the extent of actin assembly in the bud are increased in permeabilized delta cap2 cells, providing evidence that capping protein regulates the ability of the barbed ends of actin filaments to grow in yeast cells. Actin incorporation in the bud can be stimulated by treating the permeabilized cells with GTP-gamma S, and, significantly, the stimulatory effect is eliminated by a mutation in CDC42, a gene that encodes a Rho-like GTP-binding protein required for bud formation. Furthermore, the lack of actin nucleation activity in the cdc42 mutant can be complemented in vitro by a constitutively active Cdc42 protein. These results suggest that Cdc42 is closely involved in regulating actin assembly during polarized cell growth.
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Affiliation(s)
- R Li
- Department of Molecular and Cell Biology, University of California, Berkeley 94720
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