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Pederson T. Tributaries of the 2023 Nobel Prize in Physiology or Medicine, and lessons learned. RNA (NEW YORK, N.Y.) 2024; 30:101-104. [PMID: 37989583 PMCID: PMC10798239 DOI: 10.1261/rna.079874.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Accepted: 11/17/2023] [Indexed: 11/23/2023]
Abstract
Almost without exception, scientific breakthroughs are not epistemological orphans. Historians of science have developed a body of scholarship on this, and the cases arising in our era continue to confirm the phenomenon. The work by Katalin Karikó and Drew Weissman that proved foundational for the subsequent development of mRNA vaccines for COVID-19 had its antecedent roots yet is also a striking example of both serendipity and their persistence. Their receipt of the 2023 Nobel Prize in Physiology or Medicine was greatly deserved and, as Alfred Nobel likely envisioned the broad impact to be for all the prizes, affirms to the public at large that there is such a thing as the scientific method, and that there are such things as facts. The importance of society recognizing this has always been critically important, perhaps never more so than now.
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Affiliation(s)
- Thoru Pederson
- Department of Biochemistry and Molecular Biotechnology, University of Massachusetts Chan Medical School, Worcester, Massachusetts 01605, USA
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2
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Qiu L, Jing Q, Li Y, Han J. RNA modification: mechanisms and therapeutic targets. MOLECULAR BIOMEDICINE 2023; 4:25. [PMID: 37612540 PMCID: PMC10447785 DOI: 10.1186/s43556-023-00139-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Accepted: 07/28/2023] [Indexed: 08/25/2023] Open
Abstract
RNA modifications are dynamic and reversible chemical modifications on substrate RNA that are regulated by specific modifying enzymes. They play important roles in the regulation of many biological processes in various diseases, such as the development of cancer and other diseases. With the help of advanced sequencing technologies, the role of RNA modifications has caught increasing attention in human diseases in scientific research. In this review, we briefly summarized the basic mechanisms of several common RNA modifications, including m6A, m5C, m1A, m7G, Ψ, A-to-I editing and ac4C. Importantly, we discussed their potential functions in human diseases, including cancer, neurological disorders, cardiovascular diseases, metabolic diseases, genetic and developmental diseases, as well as immune disorders. Through the "writing-erasing-reading" mechanisms, RNA modifications regulate the stability, translation, and localization of pivotal disease-related mRNAs to manipulate disease development. Moreover, we also highlighted in this review all currently available RNA-modifier-targeting small molecular inhibitors or activators, most of which are designed against m6A-related enzymes, such as METTL3, FTO and ALKBH5. This review provides clues for potential clinical therapy as well as future study directions in the RNA modification field. More in-depth studies on RNA modifications, their roles in human diseases and further development of their inhibitors or activators are needed for a thorough understanding of epitranscriptomics as well as diagnosis, treatment, and prognosis of human diseases.
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Affiliation(s)
- Lei Qiu
- State Key Laboratory of Biotherapy and Cancer Center, Research Laboratory of Tumor Epigenetics and Genomics, Frontiers Science Center for Disease-Related Molecular Network, West China Hospital, Sichuan University, Chengdu, 610041, P.R. China
| | - Qian Jing
- State Key Laboratory of Biotherapy and Cancer Center, Research Laboratory of Tumor Epigenetics and Genomics, Frontiers Science Center for Disease-Related Molecular Network, West China Hospital, Sichuan University, Chengdu, 610041, P.R. China
| | - Yanbo Li
- State Key Laboratory of Biotherapy and Cancer Center, Research Laboratory of Tumor Epigenetics and Genomics, Frontiers Science Center for Disease-Related Molecular Network, West China Hospital, Sichuan University, Chengdu, 610041, P.R. China
- Department of Neurology, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Junhong Han
- State Key Laboratory of Biotherapy and Cancer Center, Research Laboratory of Tumor Epigenetics and Genomics, Frontiers Science Center for Disease-Related Molecular Network, West China Hospital, Sichuan University, Chengdu, 610041, P.R. China.
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3
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A layperson encounter, on the "modified" RNA world. Proc Natl Acad Sci U S A 2021; 118:2110706118. [PMID: 34737200 DOI: 10.1073/pnas.2110706118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2021] [Indexed: 11/18/2022] Open
Abstract
A chance conversation with a nonscientist about the mRNA-COVID vaccines, conveyed here, reminded the author of our enduring responsibility to accurately portray science to the public.
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Chen MX, Wijethunge BDIK, Zhou SM, Yang JF, Dai L, Wang SS, Chen C, Fu LJ, Zhang J, Hao GF, Yang GF. Chemical Modulation of Alternative Splicing for Molecular-Target Identification by Potential Genetic Control in Agrochemical Research. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2019; 67:5072-5084. [PMID: 30986354 DOI: 10.1021/acs.jafc.9b02086] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Alternative splicing (AS), the process of removing introns from pre-mRNA and the rearrangement of exons to produce several types of mature transcripts, is a remarkable step preceding protein synthesis. In particular, it has now been conclusively shown that up to ∼95% of genes are alternatively spliced to generate a complex and diverse proteome in eukaryotic organisms. Consequently, AS is one of the determinants of the functional repertoire of cells. Many studies have revealed that AS in plants can be regulated by cell type, developmental stage, environmental stress, and the circadian clock. Moreover, increasing amounts of evidence reveal that chemical compounds can affect various steps during splicing to induce major effects on plant physiology. Hence, the chemical modulation of AS can serve as a good strategy for molecular-target identification in attempts to potentially control plant genetics. However, the kind of mechanisms involved in the chemical modulation of AS that can be used in agrochemical research remain largely unknown. This review introduces recent studies describing the specific roles AS plays in plant adaptation to environmental stressors and in the regulation of development. We also discuss recent advances in small molecules that induce alterations of AS and the possibility of using this strategy in agrochemical-target identification, giving a new direction for potential genetic control in agrochemical research.
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Affiliation(s)
- Mo-Xian Chen
- State Key Laboratory Breeding Base of Green Pesticide and Agricultural Bioengineering; Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education; Research and Development Center for Fine Chemicals , Guizhou University , Guiyang 550025 , PR China
- Division of Gastroenterology , Shenzhen Children's Hospital , Shenzhen 518038 , PR China
- Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology , Chinese Academy of Sciences , Shenzhen 518055 , PR China
- School of Life Sciences and Shenzhen Research Institute , The Chinese University of Hong Kong , Shenzhen 518063 , PR China
| | - Boyagane D I K Wijethunge
- Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry , Central China Normal University , Wuhan 430079 , PR China
| | - Shao-Ming Zhou
- Division of Gastroenterology , Shenzhen Children's Hospital , Shenzhen 518038 , PR China
| | - Jing-Fang Yang
- Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry , Central China Normal University , Wuhan 430079 , PR China
| | - Lei Dai
- Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology , Chinese Academy of Sciences , Shenzhen 518055 , PR China
| | - Shan-Shan Wang
- School of Life Sciences and Shenzhen Research Institute , The Chinese University of Hong Kong , Shenzhen 518063 , PR China
| | - Chen Chen
- Department of Infectious Disease, Nanjing Second Hospital , Nanjing University of Chinese Medicine , Nanjing 210003 , PR China
| | - Li-Jun Fu
- Fujian Provincial Key Laboratory of Ecology-Toxicological Effects & Control for Emerging Contaminants , Putian University , Putian , Fujian 351100 , PR China
| | - Jianhua Zhang
- Department of Biology, Hong Kong Baptist University and State Key Laboratory of Agrobiotechnology , The Chinese University of Hong Kong , Shatin , Hong Kong , PR China
| | - Ge-Fei Hao
- State Key Laboratory Breeding Base of Green Pesticide and Agricultural Bioengineering; Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education; Research and Development Center for Fine Chemicals , Guizhou University , Guiyang 550025 , PR China
| | - Guang-Fu Yang
- Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry , Central China Normal University , Wuhan 430079 , PR China
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Deryusheva S, Gall JG. Orchestrated positioning of post-transcriptional modifications at the branch point recognition region of U2 snRNA. RNA (NEW YORK, N.Y.) 2018; 24:30-42. [PMID: 28974555 PMCID: PMC5733568 DOI: 10.1261/rna.063842.117] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 09/25/2017] [Indexed: 05/21/2023]
Abstract
The branch point recognition region of spliceosomal snRNA U2 is heavily modified post-transcriptionally in most eukaryotic species. We focused on this region to learn how nearby positions may interfere with each other when targeted for modification. Using an in vivo yeast Saccharomyces cerevisiae cell system, we tested the modification activity of several guide RNAs from human, mouse, the frog Xenopus tropicalis, the fruit fly Drosophila melanogaster, and the worm Caenorhabditis elegans We experimentally verified predictions for vertebrate U2 modification guide RNAs SCARNA4 and SCARNA15, and identified a C. elegans ortholog of SCARNA15. We observed crosstalk between sites in the heavily modified regions, such that modification at one site may inhibit modification at nearby sites. This is true for the branch point recognition region of U2 snRNA, the 5' loop of U5 snRNA, and certain regions of rRNAs, when tested either in yeast or in HeLa cells. The position preceding a uridine targeted for isomerization by a box H/ACA guide RNA is the most sensitive for noncanonical base-pairing and modification (either pseudouridylation or 2'-O-methylation). Based on these findings, we propose that modification must occur stepwise starting with the most vulnerable positions and ending with the most inhibiting modifications. We discuss possible strategies that cells use to reach complete modification in heavily modified regions.
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Affiliation(s)
- Svetlana Deryusheva
- Department of Embryology, Carnegie Institution for Science, Baltimore, Maryland 21218, USA
| | - Joseph G Gall
- Department of Embryology, Carnegie Institution for Science, Baltimore, Maryland 21218, USA
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6
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5-Fluorouracil Treatment Alters the Efficiency of Translational Recoding. Genes (Basel) 2017; 8:genes8110295. [PMID: 29088058 PMCID: PMC5704208 DOI: 10.3390/genes8110295] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2017] [Revised: 10/17/2017] [Accepted: 10/17/2017] [Indexed: 01/27/2023] Open
Abstract
5-fluorouracil (5-FU) is a chemotherapeutic agent that has been extensively studied since its initial development in the 1950s. It has been suggested that the mechanism of action of 5-FU involves both DNA- and RNA-directed processes, but this has remained controversial. In this study, using a series of in vivo reporter constructs capable of measuring translational recoding, we demonstrate that cells exposed to 5-FU display a reduced capacity to engage in a variety of translational recoding events, including +1 programmed frameshifting (PRF) and −1 PRF. In addition, 5-FU-treated cells are much less accurate at stop codon recognition, resulting in a significant increase in stop codon-readthrough. Remarkably, while the efficiency of cap-dependent translation appears to be unaffected by 5-FU, 5-FU-treated cells display a decreased ability to initiate cap-independent translation. We further show that knockdown of thymidylate synthase, an enzyme believed to be at the center of 5-FU-induced DNA damage, has no effect on the observed alterations in translational recoding. On the other hand, ribosomal RNA (rRNA) pseudouridylation, which plays an important role in translational recoding, is significantly inhibited. Taken together, our results suggest that the observed effect of 5-FU on recoding is an RNA-directed effect. Our results are the first to show definitely and quantitatively that translational recoding is affected by exposure to 5-FU. Thus, it is possible that a substantial portion of 5-FU cytotoxicity might possibly be the result of alterations in translational recoding efficiency.
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7
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Karijolich J, Stephenson D, Yu YT. Biochemical Purification of Box H/ACA RNPs Involved in Pseudouridylation. Methods Enzymol 2007; 425:241-62. [PMID: 17673087 DOI: 10.1016/s0076-6879(07)25011-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Box H/ACA RNPs, each consisting of four common core proteins and a single unique RNA, are the most complex pseudouridylases yet discovered. The RNA component serves as a guide that directs a target uridine for modification. To study the functions and mechanisms of RNA pseudouridylation, it is desirable to isolate the intact box H/ACA RNP complexes. Purified RNPs will allow further identification and characterization of the RNA component in each RNP complex and permit a systematic analysis of the mechanism by which the enzymes convert uridines to pseudouridines in a site-specific manner. Over the years, a number of purification techniques have been developed, providing important tools for RNA pseudouridylation research. Here, we describe three of these techniques, including biotin-streptavidin affinity purification by use of biotinylated 5-fluorouridine (5FU)-containing RNA, tandem affinity purification (TAP) by TAP-tagging one of the four core proteins in the complex, and immunoprecipitation by use of antibodies against one of the four core proteins.
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Affiliation(s)
- John Karijolich
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, NY, USA
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8
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Zhao X, Yu YT. Incorporation of 5-fluorouracil into U2 snRNA blocks pseudouridylation and pre-mRNA splicing in vivo. Nucleic Acids Res 2006; 35:550-8. [PMID: 17169984 PMCID: PMC1802618 DOI: 10.1093/nar/gkl1084] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
5-fluorouracil (5FU) is an effective anti-cancer drug, yet its mechanism of action remains unclear. Here, we examine the effect of 5FU on pre-mRNA splicing in vivo. Using RT–PCR, we show that the splicing of a number of pre-mRNAs is inhibited in HeLa cells that have been exposed to a low dose of 5FU. It appears that this inhibitory effect is not due to its incorporation into pre-mRNA, because partially or fully 5FU-substituted pre-mRNA, when injected into Xenopus oocytes, is spliced just as well as is the unsubstituted pre-mRNA. Detailed analyses of 5FU-treated cells indicate that 5FU is incorporated into U2 snRNA at important naturally occurring pseudouridylation sites. Remarkably, 5FU incorporation effectively blocks the formation of important pseudouridines in U2 snRNA, as only a trace of pseudouridine is detected when cells are exposed to a low dose of 5FU for 5 days. Injection of the hypopseudouridylated HeLa U2 snRNA into U2-depleted Xenopus oocytes fails to reconstitute pre-mRNA splicing, whereas control U2 isolated from untreated or uracil-treated HeLa cells completely reconstitutes the splicing. Our results demonstrate for the first time that 5FU incorporates into a spliceosomal snRNA at natural pseudouridylation sites in vivo, thereby inhibiting snRNA pseudouridylation and splicing. This mechanism may contribute substantially to 5FU-mediated cell death.
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Affiliation(s)
| | - Yi-Tao Yu
- To whom correspondence should be addressed. Tel: +1 585 275 1271; Fax: +1 585 275 6007;
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9
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Cao S, Chen SJ. Free energy landscapes of RNA/RNA complexes: with applications to snRNA complexes in spliceosomes. J Mol Biol 2005; 357:292-312. [PMID: 16413034 PMCID: PMC2442757 DOI: 10.1016/j.jmb.2005.12.014] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 12/02/2005] [Accepted: 12/03/2005] [Indexed: 11/24/2022]
Abstract
We develop a statistical mechanical model for RNA/RNA complexes with both intramolecular and intermolecular interactions. As an application of the model, we compute the free energy landscapes, which give the full distribution for all the possible conformations, for U4/U6 and U2/U6 in major spliceosome and U4atac/U6atac and U12/U6atac in minor spliceosome. Different snRNA experiments found contrasting structures, our free energy landscape theory shows why these structures emerge and how they compete with each other. For yeast U2/U6, the model predicts that the two distinct experimental structures, the four-helix junction structure and the helix Ib-containing structure, can actually coexist and specifically compete with each other. In addition, the energy landscapes suggest possible mechanisms for the conformational switches in splicing. For instance, our calculation shows that coaxial stacking is essential for stabilizing the four-helix junction in yeast U2/U6. Therefore, inhibition of the coaxial stacking possibly by protein-binding may activate the conformational switch from the four-helix junction to the helix Ib-containing structure. Moreover, the change of the energy landscape shape gives information about the conformational changes. We find multiple (native-like and misfolded) intermediates formed through base-pairing rearrangements in snRNA complexes. For example, the unfolding of the U2/U6 undergoes a transition to a misfolded state which is functional, while in the unfolding of U12/U6atac, the functional helix Ib is found to be the last one to unfold and is thus the most stable structural component. Furthermore, the energy landscape gives the stabilities of all the possible (functional) intermediates and such information is directly related to splicing efficiency.
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Affiliation(s)
| | - Shi-Jie Chen
- *Corresponding author, E-mail address of the corresponding author:
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10
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Xu D, Greenbaum NL, Fenley MO. Recognition of the spliceosomal branch site RNA helix on the basis of surface and electrostatic features. Nucleic Acids Res 2005; 33:1154-61. [PMID: 15728744 PMCID: PMC549433 DOI: 10.1093/nar/gki249] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
We have investigated electrostatic and surface features of an essential region of the catalytic core of the spliceosome, the eukaryotic precursor messenger (pre-m)RNA splicing apparatus. The nucleophile for the first of two splicing reactions is the 2′-hydroxyl (OH) of the ribose of a specific adenosine within the intron. During assembly of the spliceosome's catalytic core, this adenosine is positioned by pairing with a short region of the U2 small nuclear (sn)RNA to form the pre-mRNA branch site helix. The solution structure of the spliceosomal pre-mRNA branch site [Newby,M.I. and Greenbaum,N.L. (2002) Nature Struct. Biol., 9, 958–965] showed that a phylogenetically conserved pseudouridine (ψ) residue in the segment of U2 snRNA that pairs with the intron induces a markedly different structure compared with that of its unmodified counterpart. In order to achieve a more detailed understanding of the factors that contribute to recognition of the spliceosome's branch site helix and activation of the nucleophile for the first step of pre-mRNA splicing, we have calculated surface areas and electrostatic potentials of ψ-modified and unmodified branch site duplexes. There was no significant difference between the total accessible area or ratio of total polar:nonpolar groups between modified and unmodified duplexes. However, there was substantially greater exposure of nonpolar area of the adenine base, and less exposure of the 2′-OH, in the ψ-modified structure. Electrostatic potentials computed using a hybrid boundary element and finite difference nonlinear Poisson–Boltzmann approach [Boschitsch, A.H. and Fenley, M.O. (2004) J. Comput. Chem., 25, 935–955] revealed a region of exceptionally negative potential in the major groove surrounding the 2′-OH of the branch site adenosine. These surface and electrostatic features may contribute to the overall recognition of the pre-mRNA branch site region by other components of the splicing reaction.
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Affiliation(s)
- Darui Xu
- Department of Chemistry and Biochemistry, Florida State University TallahasseeFL 32306-4390, USA
| | - Nancy L. Greenbaum
- Department of Chemistry and Biochemistry, Florida State University TallahasseeFL 32306-4390, USA
- Institute of Molecular Biophysics, Florida State University TallahasseeFL 32306-4390, USA
- To whom correspondence should be addressed. Tel: +1850 644 2005; Fax: +1850 644 8281;
| | - Marcia O. Fenley
- Institute of Molecular Biophysics, Florida State University TallahasseeFL 32306-4390, USA
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Zhao X, Yu YT. Pseudouridines in and near the branch site recognition region of U2 snRNA are required for snRNP biogenesis and pre-mRNA splicing in Xenopus oocytes. RNA (NEW YORK, N.Y.) 2004; 10:681-90. [PMID: 15037777 PMCID: PMC1370558 DOI: 10.1261/rna.5159504] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Virtually all uridines in the branch site recognition region (BSRR) of vertebrate U2 are converted into pseudouridines after initial transcription. Here, we report a functional analysis of these modified nucleotides using the Xenopus oocyte reconstitution system. Using site-specific (32)P-labeling and TLC, we show that U2 pseudouridylation occurs much faster in the BSRR than in the 5'-terminal region. To functionally dissect the pseudouridines in the BSRR, we replaced each uridine with 5-fluorouridine (unmodifiable nucleotide) using site-specific RNase H cleavage directed by 2'-O-methyl-RNA-DNA chimeras followed by three-piece ligation. Whereas in vitro transcribed U2 containing no 5-fluorouridines rescued splicing in U2-depleted oocytes, no rescue was observed with U2 RNA containing 5-fluorouridines introduced into the BSRR. Additionally, U2 RNA containing 5-fluorouridines in the BSRR specifically inhibited pseudouridylation in the BSRR of in vitro transcribed U2 injected at a later time, although pseudouridylation in the 5'-end region was not affected. Our reconstitution results indicated that prior injection into U2-depleted oocytes with U2 RNA containing 5-fluorouridines in the BSRR almost completely abrogated the ability of in vitro transcribed U2 to rescue splicing, whereas full rescue was obtained with either cellular U2 or U2 containing pseudouridines in the BSRR. Further analyses using glycerol-gradient and native gel electrophoresis indicated that U2 RNAs lacking the BSRR pseudouridines do not participate in the assembly of the functionally active 17S U2 snRNP and the spliceosome. We conclude that the BSRR pseudouridines of vertebrate U2 are required for complete snRNP assembly and pre-mRNA splicing in Xenopus oocytes.
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Affiliation(s)
- Xinliang Zhao
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA
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12
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Correale P, Aquino A, Giuliani A, Pellegrini M, Micheli L, Cusi MG, Nencini C, Petrioli R, Prete SP, De Vecchis L, Turriziani M, Giorgi G, Bonmassar E, Francini G. Treatment of colon and breast carcinoma cells with 5-fluorouracil enhances expression of carcinoembryonic antigen and susceptibility to HLA-A(*)02.01 restricted, CEA-peptide-specific cytotoxic T cells in vitro. Int J Cancer 2003; 104:437-45. [PMID: 12584740 DOI: 10.1002/ijc.10969] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Cancer vaccines directed against tumor associate antigen (TAA) have produced encouraging results in preclinical models but not in cancer patients. A major limitation of this strategy is the relative degree of tolerance to these antigens and the low and heterogeneous tumor cell expression of TAA and major histocompatibility complex (MHC). Previous studies have shown that 5-fluorouracil (5-FU) can upregulate the expression of membrane-associated carcino-embryonic antigen (CEA), and MHC molecules in colon and breast carcinoma cell lines. We have investigated whether this drug can also enhance their sensitivity to the lytic effects of CEA-peptide specific Cytotoxic T cell lymphocytes (CTL). The CEA peptide-specific CTLs generated in our laboratory from normal HLA-A(*)02.01(+) donor PBMCs, were able to kill HLA-A(*)02.01(+)/CEA(+) breast (MCF-7-T103) and colon (HLA-A(*)02.01 gene-transfected HT-29 and C22.20) carcinoma cells in HLA-A(*)02.01 restricted manner. The treatment of target cells with 5-FU, enhanced their CEA expression and susceptibility to CTL-mediated lysis. Cold competition assays confirmed these results, thus supporting the hypothesis that immune target cell lysis and 5-FU mediated enhancement were dependent on CEA peptide presentation by cancer cells. 5-FU treatment of functionally "mature" CTL after in vitro expansion, did not reduce their cytolytic activity against MT-2 target cells but, when the anti-metabolite was added during the immune-sensitization phase, CTL generation was significantly inhibited. These results provide a rationale for investigating a possible new role of 5-FU as an immuno targeting amplifier agent in breast and colorectal cancer patients immunized with CEA-directed cancer vaccines.
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Ma X, Zhao X, Yu YT. Pseudouridylation (Psi) of U2 snRNA in S. cerevisiae is catalyzed by an RNA-independent mechanism. EMBO J 2003; 22:1889-97. [PMID: 12682021 PMCID: PMC154481 DOI: 10.1093/emboj/cdg191] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Pseudouridylation of snRNAs in vertebrates is guided by small nucleolar/Cajal body-specific RNAs (sno/scaRNAs). We developed an in vitro system using cell extracts and single site-radiolabeled U2 snRNAs to study pseudouridylation in Saccharomyces cerevisiae. Micrococcal nuclease-treated cell extracts are fully competent to catalyze U2 pseudouridylation, suggesting an RNA-independent process. A pseudouridylase activity for Psi(35) within yeast U2 is identified via a screen of an S.cerevisiae GST-ORF protein library. This activity is associated with YOR243c ORF, which has not previously been assigned function. When the GST-YOR243c protein is expressed in Escherichia coli, pseudouridylation activity is comparable to that expressed in S.cerevisiae, demonstrating that this protein (designated Pus7) alone can catalyze Psi(35) formation in U2. Both in vitro and in vivo analyses using wild-type and pus7-Delta strains show that Pus7 is indispensable for Psi(35) formation in U2. Using site-specific radiolabeled U2 and U2 fragments, we show that Pus7 activity is specific for Psi(35) and that the U2 stem- loop II region is essential for the pseudouridylation reaction. A BLAST search revealed Pus7 homologs in various organisms.
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Affiliation(s)
- Xiaoju Ma
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, USA
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Zhao X, Li ZH, Terns RM, Terns MP, Yu YT. An H/ACA guide RNA directs U2 pseudouridylation at two different sites in the branchpoint recognition region in Xenopus oocytes. RNA (NEW YORK, N.Y.) 2002; 8:1515-1525. [PMID: 12515384 PMCID: PMC1370357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
U2 is the most extensively modified of all spliceosomal snRNAs. We previously showed that at least some of the internally modified nucleotides in U2 snRNA are required for snRNP biogenesis and pre-mRNA splicing. Recent work from several laboratories suggests that nuclear guide RNAs facilitate U2 snRNA internal modification, including pseudouridylation and 2'-O-methylation. Here, we present a novel approach to identifying guide RNAs for U2 pseudouridylation. Several Xenopus oocyte nuclear RNAs were affinity selected with U2 snRNA substituted with 5-fluorouridine, a pseudouridylation inhibitor that sequesters pseudouridylases. One of these RNAs was sequenced and found to be a novel RNA of 134 nt. This small RNA contains an H/ACA motif and folds into a typical H/ACA RNA structure, and its authenticity as an H/ACA RNA was confirmed by immunoprecipitation analysis. The RNA contains two guide sequences for pseudouridylation (psi) of U2 snRNA at positions 34 and 44 in the branch-site recognition region, and we demonstrate that this RNA indeed guides the formation of psi34 and psi44 in U2 using a Xenopus oocyte reconstitution system. Therefore, this novel RNA was designated pugU2-34/44, for pseudouridylation guide for U2 snRNA U34 and U44. Intranuclear localization analyses indicate that pugU2-34/44 resides within the nucleoplasm rather than nucleoli or Cajal bodies where other guide RNAs have been localized. Our results clarify the mechanism of U2 snRNA pseudouridylation in Xenopus oocytes, and have interesting implications with regard to the intranuclear localization of U2 snRNA pseudouridylation.
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Affiliation(s)
- Xinliang Zhao
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA
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15
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Newby MI, Greenbaum NL. A conserved pseudouridine modification in eukaryotic U2 snRNA induces a change in branch-site architecture. RNA (NEW YORK, N.Y.) 2001; 7:833-45. [PMID: 11424937 PMCID: PMC1370140 DOI: 10.1017/s1355838201002308] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The removal of noncoding sequences (introns) from eukaryotic precursor mRNA is catalyzed by the spliceosome, a dynamic assembly involving specific and sequential RNA-RNA and RNA-protein interactions. An essential RNA-RNA pairing between the U2 small nuclear (sn)RNA and a complementary consensus sequence of the intron, called the branch site, results in positioning of the 2'OH of an unpaired intron adenosine residue to initiate nucleophilic attack in the first step of splicing. To understand the structural features that facilitate recognition and chemical activity of the branch site, duplexes representing the paired U2 snRNA and intron sequences from Saccharomyces cerevisiae were examined by solution NMR spectroscopy. Oligomers were synthesized with pseudouridine (psi) at a conserved site on the U2 snRNA strand (opposite an A-A dinucleotide on the intron strand, one of which forms the branch site) and with uridine, the unmodified analog. Data from NMR spectra of nonexchangeable protons demonstrated A-form helical backbone geometry and continuous base stacking throughout the unmodified molecule. Incorporation of psi at the conserved position, however, was accompanied by marked deviation from helical parameters and an extrahelical orientation for the unpaired adenosine. Incorporation of psi also stabilized the branch-site interaction, contributing -0.7 kcal/mol to duplex deltaG degrees 37. These findings suggest that the presence of this conserved U2 snRNA pseudouridine induces a change in the structure and stability of the branch-site sequence, and imply that the extrahelical orientation of the branch-site adenosine may facilitate recognition of this base during splicing.
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Affiliation(s)
- M I Newby
- Institute of Molecular Biophysics, Florida State University, Tallahassee 32306-4380, USA
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16
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Massenet S, Motorin Y, Lafontaine DL, Hurt EC, Grosjean H, Branlant C. Pseudouridine mapping in the Saccharomyces cerevisiae spliceosomal U small nuclear RNAs (snRNAs) reveals that pseudouridine synthase pus1p exhibits a dual substrate specificity for U2 snRNA and tRNA. Mol Cell Biol 1999; 19:2142-54. [PMID: 10022901 PMCID: PMC84007 DOI: 10.1128/mcb.19.3.2142] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Pseudouridine (Psi) residues were localized in the Saccharomyces cerevisiae spliceosomal U small nuclear RNAs (UsnRNAs) by using the chemical mapping method. In contrast to vertebrate UsnRNAs, S. cerevisiae UsnRNAs contain only a few Psi residues, which are located in segments involved in intermolecular RNA-RNA or RNA-protein interactions. At these positions, UsnRNAs are universally modified. When yeast mutants disrupted for one of the several pseudouridine synthase genes (PUS1, PUS2, PUS3, and PUS4) or depleted in rRNA-pseudouridine synthase Cbf5p were tested for UsnRNA Psi content, only the loss of the Pus1p activity was found to affect Psi formation in spliceosomal UsnRNAs. Indeed, Psi44 formation in U2 snRNA was abolished. By using purified Pus1p enzyme and in vitro-produced U2 snRNA, Pus1p is shown here to catalyze Psi44 formation in the S. cerevisiae U2 snRNA. Thus, Pus1p is the first UsnRNA pseudouridine synthase characterized so far which exhibits a dual substrate specificity, acting on both tRNAs and U2 snRNA. As depletion of rRNA-pseudouridine synthase Cbf5p had no effect on UsnRNA Psi content, formation of Psi residues in S. cerevisiae UsnRNAs is not dependent on the Cbf5p-snoRNA guided mechanism.
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Affiliation(s)
- S Massenet
- Laboratoire de Maturation des ARN et Enzymologie Moléculaire, UMR7567 CNRS-UHP, Faculté des Sciences, 54506 Vandoeuvre-les-Nancy Cédex, France
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17
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Yu YT, Shu MD, Steitz JA. Modifications of U2 snRNA are required for snRNP assembly and pre-mRNA splicing. EMBO J 1998; 17:5783-95. [PMID: 9755178 PMCID: PMC1170906 DOI: 10.1093/emboj/17.19.5783] [Citation(s) in RCA: 208] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Among the spliceosomal snRNAs, U2 has the most extensive modifications, including a 5' trimethyl guanosine (TMG) cap, ten 2'-O-methylated residues and 13 pseudouridines. At short times after injection, cellularly derived (modified) U2 but not synthetic (unmodified) U2 rescues splicing in Xenopus oocytes depleted of endogenous U2 by RNase H targeting. After prolonged reconstitution, synthetic U2 regenerates splicing activity; a correlation between the extent of U2 modification and U2 function in splicing is observed. Moreover, 5-fluorouridine-containing U2 RNA, a potent inhibitor of U2 pseudouridylation, specifically abolishes rescue by synthetic U2, while rescue by cellularly derived U2 is not affected. By creating chimeric U2 molecules in which some sequences are from cellularly derived U2 and others are from in vitro transcribed U2, we demonstrate that the functionally important modifications reside within the 27 nucleotides at the 5' end of U2. We further show that 2'-O-methylation and pseudouridylation activities reside in the nucleus and that the 5' TMG cap is not necessary for internal modification but is crucial for splicing activity. Native gel analysis reveals that unmodified U2 is not incorporated into the spliceosome. Examination of the U2 protein profile and glycerol-gradient analysis argue that U2 modifications directly contribute to conversion of the 12S to the 17S U2 snRNP particle, which is essential for spliceosome assembly.
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Affiliation(s)
- Y T Yu
- Department of Molecular Biophysics and Biochemistry, Boyer Center for Molecular Medicine, Howard Hughes Medical Institute, Yale University School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
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18
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Zerby DB, Patton JR. Modification of human U4 RNA requires U6 RNA and multiple pseudouridine synthases. Nucleic Acids Res 1997; 25:4808-15. [PMID: 9365261 PMCID: PMC147118 DOI: 10.1093/nar/25.23.4808] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Small nuclear RNAs (snRNA), cofactors in the splicing of pre-mRNA, are highly modified. In this report the modification of human U4 RNA was studied using cell extracts and in vitro synthesized, and therefore unmodified, U4 RNA. The formation of pseudouridine (Psi) at positions 4, 72 and 79 in U4 RNA was dependent on an RNA-containing cofactor, since the activities in the extracts were micrococcal nuclease (MN) sensitive. Extracts were fractionated on glycerol gradients and there was a broad peak of reconstitution activity centered at 14 S. Reconstitution was not due to additional enzymatic activity, since the peak fraction was MN sensitive. Oligodeoxynucleotide-mediated RNase H digestion of U6 RNA in the extracts inhibited formation of Psi in U4 RNA. From glycerol gradient analysis we determined that exogenously added U4 RNA that is associated with U6 RNA (sedimentation velocity 16 S) was significantly higher in Psi content than U4 RNA not associated with U6 RNA (8 S). Competitive inhibitors of Psi synthases, 5-fluorouridine-containing (5-FU) wild-type and mutant U4 RNAs, were used to investigate formation of Psi in U4 RNA. Deletions and point mutations in these 5-FU-containing U4 RNAs affected their ability to inhibit Psi synthase in vitro. With the aid of these potent inhibitors it was determined that at least two separate activities modify the uridines at these positions.
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Affiliation(s)
- D B Zerby
- Department of Pathology, School of Medicine, University of South Carolina, Columbia, SC 29208, USA
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19
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Huang Q, Jacobson MR, Pederson T. 3' processing of human pre-U2 small nuclear RNA: a base-pairing interaction between the 3' extension of the precursor and an internal region. Mol Cell Biol 1997; 17:7178-85. [PMID: 9372950 PMCID: PMC232575 DOI: 10.1128/mcb.17.12.7178] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The spliceosomal small nuclear RNAs U1, U2, U4, and U5 are transcribed by RNA polymerase II as precursors with extensions at their 3' ends. The 3' processing of these pre-snRNAs is not understood in detail. Two pathways of pre-U2 RNA 3' processing in vitro were revealed in the present investigation by using a series of human wild-type and mutant pre-U2 RNAs. Substrates with wild-type 3' ends were initially shortened by three or four nucleotides (which is the first step in vivo), and the correct mature 3' end was then rapidly generated. In contrast, certain mutant pre-U2 RNAs displayed an aberrant 3' processing pathway typified by the persistence of intermediates representing cleavage at each internucleoside bond in the precursor 3' extension. Comparison of the wild-type and mutant pre-U2 RNAs revealed a potential base-pairing interaction between nucleotides in the precursor 3' extension and a sequence located between the Sm domain and stem-loop III of U2 RNA. Substrate processing competition experiments using a highly purified pre-U2 RNA 3' processing activity suggested that only RNAs capable of this base-pairing interaction had high affinity for the pre-U2 RNA 3' processing enzyme. The importance of this postulated base-pairing interaction between the precursor 3' extension and the internal region between the Sm domain and stem-loop III was confirmed by the results obtained with a compensatory substitution that restores the base pairing, which displayed the normal 3' processing reaction. These results implicate a precursor-specific base-paired structure involving sequences on both sides of the mature cleavage site in the 3' processing of human U2 RNA.
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Affiliation(s)
- Q Huang
- Cell Biology Group, Worcester Foundation for Biomedical Research, Shrewsbury, Massachusetts 01545, USA
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20
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Temsamani J, Pederson T. The C-group heterogeneous nuclear ribonucleoprotein proteins bind to the 5' stem-loop of the U2 small nuclear ribonucleoprotein particle. J Biol Chem 1996; 271:24922-6. [PMID: 8798770 DOI: 10.1074/jbc.271.40.24922] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The C-group heterogeneous nuclear ribonucleoprotein (hnRNP) proteins bind to nascent pre-messenger RNA. In vitro studies have indicated that the C hnRNP proteins bind particularly strongly to the intron polypyrimidine tract of pre-mRNA and may be important for pre-mRNA splicing. In addition, there is evidence that the interaction of the C hnRNP proteins with pre-mRNA is facilitated by the U1 and U2 small nuclear RNPs (snRNPs). In the present study, we have uncovered another feature of the C hnRNP proteins that may provide a unifying framework for these previous observations; the C hnRNP proteins bind to the 5' stem-loop of the U2 snRNP. This was detected by incubating human 32P-labeled U2 snRNP in micrococcal nuclease-treated HeLa nuclear extracts, followed by UV-mediated protein-RNA cross-linking, which revealed that C hnRNP proteins were cross-linked to 32P-nucleotides in the U2 snRNP. In similar experiments, no cross-linking of C hnRNP proteins to 32P-labeled U1 or U4 snRNPs was observed. The observed cross-linking of C hnRNP proteins to U2 snRNP was efficiently competed by excess U2 RNA and by poly(U) but not by poly(A). No competition was observed with an RNA molecule comprising U2 nucleotides 105-189, indicating that the C hnRNP protein interactive regions of U2 RNA reside solely in the 5' half of the molecule. Oligodeoxynucleotide-mediated RNase H cleavage experiments revealed that a 5' region of U2 RNA including nucleotides 15-28 is essential for the observed C hnRNP protein cross-linking. C hnRNP protein cross-linking to U2 snRNP was efficiently competed by a mini-RNA corresponding to the first 29 nucleotides of U2 RNA, whereas no competition was observed with a variant of this mini-RNA in which the UUUU loop of stem-loop I was mutationally configured into a single-stranded RNA by replacing the stem with non-pairing nucleotides. Competition experiments with another mutant mini-U2 RNA in which the UUUU loop was replaced by AAAA indicated that both the UUUU loop and the stem are important for C hnRNP protein cross-linking, a finding consistent with other recent data on the RNA sequence specificity of C hnRNP protein binding.
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Affiliation(s)
- J Temsamani
- Cell Biology Group, Worcester Foundation for Biomedical Research, Shrewsbury, Massachusetts 01545, USA
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21
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Zerby DB, Patton JR. Metabolism of pre-messenger RNA splicing cofactors: modification of U6 RNA is dependent on its interaction with U4 RNA. Nucleic Acids Res 1996; 24:3583-9. [PMID: 8836186 PMCID: PMC146130 DOI: 10.1093/nar/24.18.3583] [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: 02/02/2023] Open
Abstract
The requirements for the formation of pseudouridine (psi) in U4 and U6 RNAs, cofactors in the splicing of pre-messenger RNA, were investigated in vitro using HeLa nuclear (NE) and cytoplasmic (S100) extracts. Maximal psi formation for both RNAs was extract order-dependent. Maximal psi formation in U4 RNA required incubation in S100 followed by the addition of NE, paralleling the in vivo maturation pathway of U4 RNA. In contrast, maximal formation of psi in U6 RNA required incubation in NE followed by the addition of S100 extract. Since U6 RNA does not exit the nucleus in vivo the contribution of S100 was investigated. In experiments where the extracts were treated with micrococcal nuclease to digest endogenous snRNAs, the efficient formation of psi in U6 RNA was dependent on the presence of U4 RNA, but not in U5 RNA or tRNA. When mutant U4 RNAs that inhibit or strengthen the interaction between U4 RNA, and U6 RNA were substituted for wild-type U4 RNA, the results confirmed the need for the interaction between these two RNAs for psi formation in U6 RNA. U6 RNA isolated from glycerol gradients after incubation in extracts had four times as much psi when associated with U4 RNA.
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Affiliation(s)
- D B Zerby
- Department of Pathology, School of Medicine, University of South Carolina, Columbia 29208, USA
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22
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Koonin EV. Pseudouridine synthases: four families of enzymes containing a putative uridine-binding motif also conserved in dUTPases and dCTP deaminases. Nucleic Acids Res 1996; 24:2411-5. [PMID: 8710514 PMCID: PMC145960 DOI: 10.1093/nar/24.12.2411] [Citation(s) in RCA: 171] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Using a combination of several methods for protein sequence comparison and motif analysis, it is shown that the four recently described pseudouridine syntheses with different specificities belong to four distinct families. Three of these families share two conserved motifs that are likely to be directly involved in catalysis. One of these motifs is detected also in two other families of enzymes that specifically bind uridine, namely deoxycitidine triphosphate deaminases and deoxyuridine triphosphatases. It is proposed that this motif is an essential part of the uridine-binding site. Two of the pseudouridine syntheses, one of which modifies the anticodon arm of tRNAs and the other is predicted to modify a portion of the large ribosomal subunit RNA belonging to the peptidyltransferase center, are encoded in all extensively sequenced genomes, including the 'minimal' genome of Mycoplasma genitalium. These particular RNA modifications and the respective enzymes are likely to be essential for the functioning of any cell.
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Affiliation(s)
- E V Koonin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
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23
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Shimba S, Bokar JA, Rottman F, Reddy R. Accurate and efficient N-6-adenosine methylation in spliceosomal U6 small nuclear RNA by HeLa cell extract in vitro. Nucleic Acids Res 1995; 23:2421-6. [PMID: 7630720 PMCID: PMC307046 DOI: 10.1093/nar/23.13.2421] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Human U6 small nuclear RNA (U6 snRNA), an abundant snRNA required for splicing of pre-mRNAs, contains several post-transcriptional modifications including a single m6A (N-6-methyladenosine) at position 43. This A-43 residue is critical for the function of U6 snRNA in splicing of pre-mRNAs. Yeast and plant U6 snRNAs also contain m6A in the corresponding position showing that this modification is evolutionarily conserved. In this study, we show that upon incubation of an unmodified U6 RNA with HeLa cell extract, A-43 residue in human U6 snRNA was rapidly converted to m6A-43. This conversion was detectable as early as 3 min after incubation and was nearly complete in 60 min; no other A residue in U6 snRNA was converted to m6A. Deletion studies showed that the stem-loop structure near the 5' end of U6 snRNA is dispensable for m6A formation; however, the integrity of the 3' stem-loop was necessary for efficient m6A formation. These data show that a short stretch of primary sequence flanking the methylation site is not sufficient for U6 m6A methyltransferase recognition and the enzyme probably recognizes secondary and/or tertiary structural features in U6 snRNA. The enzyme that catalyzes m6A formation in U6 snRNA appears to be distinct from the prolactin mRNA methyltransferase which is also present in HeLa nuclear extracts.
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Affiliation(s)
- S Shimba
- Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA
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24
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Abstract
The formation of pseudouridine (psi) on U5 small nuclear RNA (U5 snRNA) was studied using an in vitro modification system. Labeled U5 RNA, synthesized in vitro and therefore unmodified, was incubated in reactions containing S100 and/or nuclear extracts (NE) from HeLa cells, and the levels of psi were determined. There are three psi residues found in human U5 RNA, at positions 43, 46, and 53. Incubation of unmodified U5 RNA in reactions containing either S100 or NE supports psi formation at positions 43 and 46, which are found in a loop in the predicted secondary structure of U5 RNA. However, psi formation at position 53, which is found in a stem, is dependent on the presence of NE during the incubation. The order of extract addition does not have a significant effect on the formation of psi at position 53 as long as NE is present. The most efficient psi formation was observed with a combination of S100 and NE which allowed for efficient small nuclear ribonucleoprotein particle (snRNP) assembly and psi formation. When 9S and 20S U5 snRNPs were isolated by velocity sedimentation gradient centrifugation after incubation in the combined extracts, there was little difference in the psi levels at any of the positions for the two distinct particles. Mutations in the U5 RNA sequence do affect psi formation. U5 RNAs that have mutated Sm binding sites or are truncated prior to the Sm binding site have very low levels of psi formation at positions 43 and 46 and no detectable psi formation at position 53. A deletion of five nucleotides from 39 to 43 abolishes psi formation at positions 43 and 46, but the modification of position 53 is unaffected.
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Affiliation(s)
- J R Patton
- Department of Pathology, School of Medicine, University of South Carolina, Columbia 29208
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