Sequence and expression patterns of a human EMAP-related protein-2 (HuEMAP-2)

QTL mapping of human retina DNA methylation identifies 87 gene-epigenome interactions in age-related macular degeneration

DNA methylation provides a crucial epigenetic mark linking genetic variations to environmental influence. We have analyzed array-based DNA methylation profiles of 160 human retinas with co-measured RNA-seq and >8 million genetic variants, uncovering sites of genetic regulation in cis (37,453 methylation quantitative trait loci and 12,505 expression quantitative trait loci) and 13,747 DNA methylation loci affecting gene expression, with over one-third specific to the retina. Methylation and expression quantitative trait loci show non-random distribution and enrichment of biological processes related to synapse, mitochondria, and catabolism. Summary data-based Mendelian randomization and colocalization analyses identify 87 target genes where methylation and gene-expression changes likely mediate the genotype effect on age-related macular degeneration. Integrated pathway analysis reveals epigenetic regulation of immune response and metabolism including the glutathione pathway and glycolysis. Our study thus defines key roles of genetic variations driving methylation changes, prioritizes epigenetic control of gene expression, and suggests frameworks for regulation of macular degeneration pathology by genotype-environment interaction in retina.

QTL mapping of human retina DNA methylation identifies 87 gene-epigenome interactions in age-related macular degeneration

DNA methylation (DNAm) provides a crucial epigenetic mark linking genetic variations to environmental influence. We analyzed array-based DNAm profiles of 160 human retinas with co-measured RNA-seq and > 8 million genetic variants, uncovering sites of genetic regulation in cis (37,453 mQTLs and 12,505 eQTLs) and 13,747 eQTMs (DNAm loci affecting gene expression), with over one-third specific to the retina. mQTLs and eQTMs show non-random distribution and enrichment of biological processes related to synapse, mitochondria, and catabolism. Summary data-based Mendelian randomization and colocalization analyses identify 87 target genes where methylation and gene-expression changes likely mediate the genotype effect on age-related macular degeneration (AMD). Integrated pathway analysis reveals epigenetic regulation of immune response and metabolism including the glutathione pathway and glycolysis. Our study thus defines key roles of genetic variations driving methylation changes, prioritizes epigenetic control of gene expression, and suggests frameworks for regulation of AMD pathology by genotype-environment interaction in retina.

Molecular Anatomy of the EML4-ALK Fusion Protein for the Development of Novel Anticancer Drugs

The EML4 (echinoderm microtubule-associated protein-like 4)-ALK (anaplastic lymphoma kinase) fusion gene in non-small-cell lung cancer (NSCLC) was first identified in 2007. As the EML4-ALK fusion protein promotes carcinogenesis in lung cells, much attention has been paid to it, leading to the development of therapies for patients with NSCLC. These therapies include ALK tyrosine kinase inhibitors and heat shock protein 90 inhibitors. However, detailed information on the entire structure and function of the EML4-ALK protein remains deficient, and there are many obstacles to overcome in the development of novel anticancer agents. In this review, we describe the respective partial structures of EML4 and ALK that are known to date. In addition to their structures, noteworthy structural features and launched inhibitors of the EML4-ALK protein are summarized. Furthermore, based on the structural features and inhibitor-binding modes, we discuss strategies for the development of novel inhibitors targeting the EML4-ALK protein.

EML2-S constitutes a new class of proteins that recognizes and regulates the dynamics of tyrosinated microtubules

Tubulin post-translational modifications (PTMs) alter microtubule properties by affecting the binding of microtubule-associated proteins (MAPs). Microtubule detyrosination, which occurs by proteolytic removal of the C-terminal tyrosine from ɑ-tubulin, generates the oldest known tubulin PTM, but we lack comprehensive knowledge of MAPs that are regulated by this PTM. We developed a screening pipeline to identify proteins that discriminate between Y- and ΔY-microtubules and found that echinoderm microtubule-associated protein-like 2 (EML2) preferentially interacts with Y-microtubules. This activity depends on a Y-microtubule interaction motif built from WD40 repeats. We show that EML2 tracks the tips of shortening microtubules, a behavior not previously seen among human MAPs in vivo, and influences dynamics to increase microtubule stability. Our screening pipeline is readily adapted to identify proteins that specifically recognize a wide range of microtubule PTMs.

Mitotic phosphorylation by NEK6 and NEK7 reduces the microtubule affinity of EML4 to promote chromosome congression

EML4 is a microtubule-associated protein that promotes microtubule stability. We investigated its regulation across the cell cycle and found that EML4 was distributed as punctate foci along the microtubule lattice in interphase but exhibited reduced association with spindle microtubules in mitosis. Microtubule sedimentation and cryo-electron microscopy with 3D reconstruction revealed that the basic N-terminal domain of EML4 mediated its binding to the acidic C-terminal tails of α- and β-tubulin on the microtubule surface. The mitotic kinases NEK6 and NEK7 phosphorylated the EML4 N-terminal domain at Ser144 and Ser146 in vitro, and depletion of these kinases in cells led to increased EML4 binding to microtubules in mitosis. An S144A-S146A double mutant not only bound inappropriately to mitotic microtubules but also increased their stability and interfered with chromosome congression. In addition, constitutive activation of NEK6 or NEK7 reduced the association of EML4 with interphase microtubules. Together, these data support a model in which NEK6- and NEK7-dependent phosphorylation promotes the dissociation of EML4 from microtubules in mitosis in a manner that is required for efficient chromosome congression.

Microtubule-Associated Proteins: Structuring the Cytoskeleton

Microtubule-associated proteins (MAPs) were initially discovered as proteins that bind to and stabilize microtubules. Today, an ever-growing number of MAPs reveals a more complex picture of these proteins as organizers of the microtubule cytoskeleton that have a large variety of functions. MAPs enable microtubules to participate in a plethora of cellular processes such as the assembly of mitotic and meiotic spindles, neuronal development, and the formation of the ciliary axoneme. Although some subgroups of MAPs have been exhaustively characterized, a strikingly large number of MAPs remain barely characterized other than their interactions with microtubules. We provide a comprehensive view on the currently known MAPs in mammals. We discuss their molecular mechanisms and functions, as well as their physiological role and links to pathologies.

EML proteins in microtubule regulation and human disease

The EMLs are a conserved family of microtubule-associated proteins (MAPs). The founding member was discovered in sea urchins as a 77-kDa polypeptide that co-purified with microtubules. This protein, termed EMAP for echinoderm MAP, was the major non-tubulin component present in purified microtubule preparations made from unfertilized sea urchin eggs [J. Cell Sci. (1993) 104, 445–450; J. Cell Sci. (1987) 87(Pt 1), 71–84]. Orthologues of EMAP were subsequently identified in other echinoderms, such as starfish and sand dollar, and then in more distant eukaryotes, including flies, worms and vertebrates, where the name of ELP or EML (both for EMAP-like protein) has been adopted [BMC Dev. Biol. (2008) 8, 110; Dev. Genes Evol. (2000) 210, 2–10]. The common property of these proteins is their ability to decorate microtubules. However, whether they are associated with particular microtubule populations or exercise specific functions in different microtubule-dependent processes remains unknown. Furthermore, although there is limited evidence that they regulate microtubule dynamics, the biochemical mechanisms of their molecular activity have yet to be explored. Nevertheless, interest in these proteins has grown substantially because of the identification of EML mutations in neuronal disorders and oncogenic fusions in human cancers. Here, we summarize our current knowledge of the expression, localization and structure of what is proving to be an interesting and important class of MAPs. We also speculate about their function in microtubule regulation and highlight how the studies of EMLs in human diseases may open up novel avenues for patient therapy.

Microtubule association of EML proteins and the EML4-ALK variant 3 oncoprotein require an N-terminal trimerization domain

Proteins of the echinoderm microtubule (MT)-associated protein (EMAP)-like (EML) family contribute to formation of the mitotic spindle and interphase MT network. EML1-4 consist of Trp-Asp 40 (WD40) repeats and an N-terminal region containing a putative coiled-coil. Recurrent gene rearrangements in non-small cell lung cancer (NSCLC) fuse EML4 to anaplastic lymphoma kinase (ALK) causing expression of several oncogenic fusion variants. The fusions have constitutive ALK activity due to self-association through the EML4 coiled-coil. We have determined crystal structures of the coiled-coils from EML2 and EML4, which describe the structural basis of both EML self-association and oncogenic EML4-ALK activation. The structures reveal a trimeric oligomerization state directed by a conserved pattern of hydrophobic residues and salt bridges. We show that the trimerization domain (TD) of EML1 is necessary and sufficient for self-association. The TD is also essential for MT binding; however, this property requires an adjacent basic region. These observations prompted us to investigate MT association of EML4-ALK and EML1-ABL1 (Abelson 1) fusions in which variable portions of the EML component are present. Uniquely, EML4-ALK variant 3, which includes the TD and basic region of EML4 but none of the WD40 repeats, was localized to MTs, both when expressed recombinantly and when expressed in a patient-derived NSCLC cell line (H2228). This raises the question of whether the mislocalization of ALK activity to MTs might influence downstream signalling and malignant properties of cells. Furthermore, the structure of EML4 TD may enable the development of protein-protein interaction inhibitors targeting the trimerization interface, providing a possible avenue towards therapeutic intervention in EML4-ALK NSCLC.

Crystal structure of EML1 reveals the basis for Hsp90 dependence of oncogenic EML4-ALK by disruption of an atypical β-propeller domain

Proteins of the echinoderm microtubule-associated protein (EMAP)-like (EML) family contribute to formation of the mitotic spindle and interphase microtubule network. They contain a unique hydrophobic EML protein (HELP) motif and a variable number of WD40 repeats. Recurrent gene rearrangements in nonsmall cell lung cancer fuse EML4 to anaplastic lymphoma kinase (ALK), causing expression of several fusion oncoprotein variants. We have determined a 2.6-Å crystal structure of the representative ∼70-kDa core of EML1, revealing an intimately associated pair of β-propellers, which we term a TAPE (tandem atypical propeller in EMLs) domain. One propeller is highly atypical, having a discontinuous subdomain unrelated to a WD40 motif in place of one of its blades. This unexpected feature shows how a propeller structure can be assembled from subdomains with distinct folds. The HELP motif is not an independent domain but forms part of the hydrophobic core that joins the two β-propellers. The TAPE domain binds α/β-tubulin via its conserved, concave surface, including part of the atypical blade. Mapping the characteristic breakpoints of each EML4-ALK variant onto our structure indicates that the EML4 TAPE domain is truncated in many variants in a manner likely to make the fusion protein structurally unstable. We found that the heat shock protein 90 (Hsp90) inhibitor ganetespib induced degradation of these variants whereas others lacking a partial TAPE domain were resistant in both overexpression models and patient-derived cell lines. The Hsp90-sensitive EML4-ALK variants are exceptions to the rule that oncogenic fusion proteins involve breakpoints in disordered regions of both partners.

Prenatal smoke exposure: effects on infant auditory system and placental gene expression

Prenatal smoke exposure has been shown to change cochlear echo response amplitudes and auditory brainstem response (ABR) wave latencies in newborns. Since gene expression changes are often synchronized in different tissue types, the goal of the present work was to determine the relationships between prenatal smoke exposure induced changes in hearing responses with changes in placental gene expression. Results showed significant cotinine level elevations in mothers who smoked ≥10cigarettes/day during their pregnancy compared to no detectable cotinine in nonsmoking mothers. Cochlear echo response amplitudes in the 2-8kHz range and ABR wave latencies, specifically wave V and interpeak interval I-V, were also significantly reduced in newborns of smoking mothers. Functional pathway analysis of upregulated placental genes using the Database for Annotation, Visualization and Integrated Discovery (DAVID) online software showed significant enrichment of terms associated with neurodevelopmental processes including glutamatergic and cholinergic systems and a number of wingless type proteins in the top two tiers with corrected enrichment p-values of ≤0.05. Other relevant functional pathways were significant at unadjusted enrichment p-values of 0.001-0.11 and included calcium signaling, neurotransmission/neurological processes and oxidative stress. The neurological process clusters included 7 genes (EML2, OTOR, SLC26A5, TBL1X, TECTA, USH1C and USH1G) known to modulate cochlear outer hair cell motility. We localized proteins encoded by the top two regulated genes, TBL1X and USH1C, using immunohistochemistry to placental stem and anchoring villi associated with active contractile function. These placental genes may mediate active contraction and relaxation in the placental villi, for example, during maternal-fetal perfusion matching, similar to the active lengthening and shortening of the cochlear outer hair cells during sensory transduction. Thus, the functional consequence of their alteration in the cochlea would be reflected as a decline in cochlear echoes as shown in this study. Such parallel changes suggest the potential utility of placental gene expression as a surrogate for evaluating changes in the developing cochlea related to potential aberrant cochlear function in newborns with prenatal smoke exposure.

Changes in oxygen and carbon dioxide environment alter gene expression of cowpea bruchids

Hermetic storage is a widely adopted technique for preventing stored grain from being damaged by storage insect pests. In the air-tight container, insects consume oxygen through metabolism while concomitantly raising carbon dioxide concentrations through respiration. Previous studies on the impact of hypoxia and hypercapnia on feeding behavior of cowpea bruchids have shown that feeding activity gradually decreases in proportion to the changing gas concentrations and virtually ceases at approximately 3-6% (v/v) oxygen and 15-18% carbon dioxide. Further, a number of bruchid larvae are able to recover their feeding activity after days of low oxygen and high carbon dioxide, although extended exposure tends to reduce survival. In the current study, to gain insight into the molecular mechanism underpinning the hypoxia-coping response, we profiled transcriptomic responses to hypoxia/hypercapnia (3% oxygen, 17% carbon dioxide for 4 and 24h) using cDNA microarrays, followed by quantitative RT-PCR verification of selected gene expression changes. A total of 1046 hypoxia-responsive cDNAs were sequenced; these clustered into 765 contigs, of which 645 were singletons. Many (392) did not show homology with known genes, or had homology only with genes of unknown function in a BLAST search. The identified differentially-regulated sequences encoded proteins presumptively involved in nutrient transport and metabolism, cellular signaling and structure, development, and stress responses. Gene expression profiles suggested that insects compensate for lack of oxygen by coordinately reducing energy demand, shifting to anaerobic metabolism, and strengthening cellular structure and muscular contraction.

The C. elegans EMAP-like protein, ELP-1 is required for touch sensation and associates with microtubules and adhesion complexes

Background

The founding member of the EMAP-like protein family is the Echinoderm Microtubule-Associated Protein (EMAP), so-named for its abundance in sea urchin, starfish, and sand dollar eggs. The EMAP-like protein family has five members in mammals (EML1 through EML5) and only one in both Drosophila (ELP-1) and C. elegans (ELP-1). Biochemical studies of sea urchin EMAP and vertebrate EMLs implicate these proteins in the regulation of microtubule stability. So far, however, the physiological function of this protein family remains unknown.

Results

We examined the expression pattern of C. elegans ELP-1 by means of transgenic gene expression in living embryos and adults, and by immunolocalization with an ELP-1-specific antibody in fixed tissues. In embryos, ELP-1 is expressed in the hypodermis. In larvae and adults, ELP-1 is expressed in the body wall, spermatheca and vulval muscles, intestine, and hypodermal seam cells. In muscle, ELP-1 is associated with adhesion complexes near the cell surface and is bound to a criss-crossing network of microtubules in the cytoplasm. ELP-1 is also expressed in a subset of mechanoreceptor neurons, including the ray neurons in the male tail, microtubule-rich touch receptor neurons, and the six ciliated IL1 neurons. This restricted localization in the nervous system implies that ELP-1 plays a role in mechanotransmission. Consistent with this idea, decreasing ELP-1 expression decreases sensitivity to gentle touch applied to the body wall.

Conclusion

These data imply that ELP-1 may play an important role during the transmission of forces and signals between the body surface and both muscle cells and touch receptor neurons.

Echinoderm microtubule-associated protein like protein 4, a member of the echinoderm microtubule-associated protein family, stabilizes microtubules

Echinoderm microtubule-associated protein (EMAP) is the major microtubule binding protein in dividing sea urchin (Strongylocentrotus purpuratus) eggs. Echinoderm microtubule-associated protein like protein 4 (Eml4, restrictedly overexpressed proliferation-associated protein 120 kDa (Ropp120)) is one of the five mammalian EMAP homologues, the cellular function of which remains to be elucidated. In our first set of experiments we determined the spatio-temporal expression pattern of Eml4 in mouse brain. Our results demonstrate that Eml4 is a highly developmentally regulated gene with high expression levels in the developing nervous system of E11 embryos declining to low levels in adult. Spatially, Eml4 expression becomes restricted to the olfactory bulb, hippocampus and cerebellum. Transient transfection of a fusion construct of full-length mouse Eml4 with green fluorescent protein (GFP-Eml4) into Cos7 and HeLa cells resulted in colocalization of GFP-Eml4 with microtubules. This colocalization was observed both with microtubules of non-dividing cells and with the mitotic spindle of dividing cells. In addition, transient overexpression of GFP-Eml4 in Cos7 cells resulted in microtubules that were resistant to nocodazole treatment suggesting that Eml4 stabilizes microtubules. A consequence of microtubule stabilization is a net reduction in the amount of free tubulin. Microtubule stabilizing proteins therefore are expected to indirectly decrease the microtubule growth rate. Indeed, transient transfection of GFP-Eml4 resulted in a marked decrease in the microtubule growth rate, which is in line with our hypothesis that Eml4 functions as a microtubule stabilizing protein. In summary, our results suggest that Eml4 is a developmentally regulated protein that colocalizes with and stabilizes microtubules.

Human EML4, a novel member of the EMAP family, is essential for microtubule formation

Human EML4 (EMAP-like protein 4) is a novel microtubule-associated WD-repeat protein of 120 kDa molecular weight, which is classified as belonging to the conserved family of EMAP-like proteins. Cosedimentation assays demonstrated that EML4 associates with in vitro polymerized microtubules. Correspondingly, immunofluorescence stainings and transient expression of EGFP-labeled EML4 revealed a complete colocalization of EML4 with the interphase microtubule array of HeLa cells. We present evidence that the amino-terminal portion of EML4 (amino acids 1-249) is essential for the association with microtubules. Immunoprecipitation experiments revealed that EML4 is hyperphosphorylated on serine/threonine residues during mitosis. In addition, immunofluorescence stainings demonstrated that hyperphosphorylated EML4 is associated with the mitotic spindle, suggesting that the function of EML4 is regulated by phosphorylation. siRNA-mediated knockdown of EML4 in HeLa cells led to a significant decrease in the number of cells. In no case mitotic figures could be observed in EML4 negative HeLa cells. Additionally, we observed a significant reduction of the proliferation rate and the uptake of radioactive [3H]-thymidine as a result of EML4 silencing. Most importantly, EML4 negative cells showed a completely modified microtubule network, indicating that EML4 is necessary for correct microtubule formation.

Eml5, a novel WD40 domain protein expressed in rat brain

We have isolated a novel transcript with homology to the major microtubule-associated protein in dividing sea urchin embryos, EMAP. The protein has a predicted MW of approximately 180 kDa and we have named it Eml5 (EMAP-like protein 5). Eml5 contains 11 putative WD40 domains and 3 hydrophobic stretches of 43 aa, HELP domains, which have been suggested to be involved in microtubule binding. Eml5 appears to consist of two tandem repeats of the complete EMAP protein separated by a putative dimerization domain. Eml5 mRNA and protein is expressed at high levels in the hippocampus, cerebellum and olfactory bulb, as determined by in situ hybridization and immunocytochemistry. Eml5 transcripts can be detected in fore- and hindbrain structures from embryonic day 13 onwards. Because other EMAP-like proteins are involved in regulating microtubule dynamics, it is likely that Eml5 plays a role in the regulation of cytoskeletal rearrangements during neuronal development and in adult brain

Regulation of microtubule-associated proteins

Microtubule-associated proteins (MAPs) function to regulate the assembly dynamics and organization of microtubule polymers. Upstream regulation of MAP activities is the major mechanism used by cells to modify and control microtubule assembly and organization. This review summarizes the functional activities of MAPs found in animal cells and discusses how these MAPs are regulated. Mechanisms controlling gene expression, isoform-specific expression, protein localization, phosphorylation, and degradation are discussed. Additional regulatory mechanisms include synergy or competition between MAPs and the activities of cofactors or binding partners. For each MAP it is likely that regulation in vivo reflects a composite of multiple regulatory mechanisms.

Identification of rat EMAP, a delta-glutamate receptor binding protein

While most subtypes of glutamate receptors have been studied extensively, less is known about the delta-glutamate receptors, delta1 and delta2. Although neither forms functional channels when expressed in heterologous cells, genetic analyses have demonstrated the physiological significance of delta2. We used the cytosolic C-terminus of the delta2 glutamate receptor subunit in a yeast two-hybrid screen of a rat brain cDNA library to identify delta-glutamate receptor binding proteins. We isolated rat EMAP, the rat homolog of a microtubule-associated protein initially isolated and characterized in echinoderms. Rat EMAP contains 10 WD-repeats, which are domains important for mediating protein-protein interactions in a wide variety of proteins. Rat EMAP binds to delta-glutamate receptor subunits within a 50-amino-acid segment of the delta C-terminus. It is widely expressed in both brain and peripheral tissues, including high expression in brainstem and enrichment in the postsynaptic density.

The human EMAP-like protein-70 (ELP70) is a microtubule destabilizer that localizes to the mitotic apparatus

In this report, we show that the echinoderm microtubule (MT)-associated protein (EMAP) and related EMAP-like proteins (ELPs) share a similar domain organization with a highly conserved hydrophobic ELP (HELP) domain and a large tryptophan-aspartic acid (WD) repeat domain. To determine the function of mammalian ELPs, we generated antibodies against a 70-kDa human ELP and showed that ELP70 coassembled with MTs in HeLa cell extracts and colocalized with MTs in the mitotic apparatus. To determine whether ELP70 bound to MTs directly, human ELP70 was expressed and purified to homogeneity from baculovirus-infected Sf9 cells. Purified ELP70 bound to purified MTs with a stoichiometry of 0.40 +/- 0.04 mol of ELP70/mol of tubulin dimer and with an intrinsic dissociation constant of 0.44 +/- 0.13 microm. Using a nucleated assembly assay and video-enhanced differential interference contrast microscopy, we demonstrated that ELP70 reduced seeded nucleation, reduced the growth rate, and promoted MT catastrophes in a concentration-dependent manner. As a result, ELP70-containing MTs were significantly shorter than MTs assembled from tubulin alone. These data indicate that ELP70 is a novel MT destabilizer. A lateral destabilization model is presented to describe ELP70's effects on microtubules.

Saturable binding of the echinoderm microtubule-associated protein (EMAP) on microtubules, but not filamentous actin or vimentin filaments

The echinoderm microtubule-associated protein (EMAP) is a 75-kDa, WD-repeat protein associated with the mitotic spindle apparatus. To understand EMAP's biological role, it is important to determine its affinity for microtubules (MTs) and other cytoskeletal components. To accomplish this goal, we utilized a low-cost, bubble-column bioreactor to express EMAP as a hexahistidine fusion (6his) protein in baculovirus-infected insect cells. After optimizing cell growth conditions, up to 30 mg of EMAP was obtained in the soluble cell lysate from a 1-liter culture. EMAP was purified to homogeneity in a two-step process that included immobilized metal-affinity chromatography (IMAC) and anion-exchange chromatography. In vitro binding studies on cytoskeletal components were performed with the 6his-EMAP. EMAP bound to MTs, but not actin or vimentin filaments, with an intrinsic dissociation constant of 0.18 microM and binding stoichiometry of 0.7 mol EMAP per mol tubulin heterodimer. In addition, we show that a strong MT binding domain resides in the 137 amino acid, NH(2)-terminus of EMAP and a weaker binding site in the WD-domain. Previous work has shown that the EMAP concentration in the sea urchin egg is over 4 microM. Together, these results show that there is sufficient EMAP in the egg to regulate the assembly of a large pool of maternally stored tubulin.

Rapid dynamics of the microtubule binding of ensconsin in vivo

Microtubule-associated proteins (MAPs) are proteins that reversibly bind to and regulate microtubule dynamics and functions in vivo. We examined the dynamics of binding of a MAP called ensconsin (E-MAP-115) to microtubules in vivo. We used 5×GFP-EMTB, a construct in which the microtubule-binding domain of ensconsin (EMTB) is fused to five copies of green fluorescent protein (GFP), as a reporter molecule amenable to the use of fluorescent speckle microscopy. Fluorescent speckle microscopy (FSM) sequences and kymograph analyses showed rapid dynamics of speckles comprised of 5×GFP-EMTB in untreated cells. By contrast, in detergent-lysed cytoskeletons, speckles were not dynamic. Since detergent-lysed cytoskeletons differ from living cells in that they lack both ATP and dynamic microtubules, we used azide treatment to substantially reduce the level of ATP in living cells and we used Taxol to halt microtubule dynamics. Both treatments slowed the dynamics of 5×GFP-EMTB speckles observed by FSM. We also used fluorescence recovery after photobleaching (FRAP) to quantify the half-time of binding and dissociation of the 5×GFP-EMTB chimera and to compare this half-time to that of the full-length MAP molecule. In untreated cells, the tg of either 5×GFP-EMTB or full-length GFP-ensconsin was similarly rapid (∼4 seconds), while in ATP-reduced and Taxol-treated cells, tg was increased to 210 seconds and 40 seconds, respectively. In detergent-extracted cells no recovery was seen. Consistent with the rapid dynamics of 5×GFP-EMTB measured with fluorescent speckle microscopy and FRAP, we estimated that the affinity of the MAP for microtubules is ∼40 μM in untreated living cells, compared with ∼1 μM in vitro. However, KD,app was not significantly changed in the presence of azide and was increased to 110 μM in the presence of Taxol. To test whether changes in the phosphorylation state of cellular proteins might be responsible for altering the dynamics of ensconsin binding, we used FSM to monitor staurosporine-treated cells. Staurosporine treatment substantially halted dynamics of 5×GFP-EMTB speckles along MTs. Our results show that ensconsin is highly dynamic in its association with microtubules, and its microtubule association can be altered by in vivo phosphorylation events.

Cloning and localization of C2orf2(ropp120), a previously unknown WD repeat protein

Ropp 120 (restrictedly overexpressed proliferation-associated protein) is a cytoplasmic protein of 120 kDa that is significantly overexpressed in mitotic cells. Protein sequencing of the immunoaffinity purified 120-kDa protein showed it to be an as yet unknown protein. DNA sequencing revealed a cDNA sequence of 3419 bases, which includes the complete coding region of ropp120 of 2943 bases (981 amino acids). Analysis of the deduced amino acid sequence showed that ropp 120 contains four WD repeats and a well-conserved consensus sequence of serine proteases. The gene encoding ropp120 (HGMW-approved gene symbol C2orf2) was assigned to chromosome 2p21-p22 by means of radiation hybrid and fluorescence in situ hybridization mapping.