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David E Sterner

Publications and source records attributed to David E Sterner.

7 recordsLinked to original sources
PubMed2006

Histone sumoylation is a negative regulator in Saccharomyces cerevisiae and shows dynamic interplay with positive-acting histone modifications.

Covalent histone post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitylation play pivotal roles in regulating many cellular processes, including transcription, response to DNA damage, and epigenetic control. Although positive-acting post-translational modifications have been studied in Saccharomyces cerevisiae, histone modifications that are associated with transcriptional repression have not been shown to occur in this yeast. Here, we provide evidence that histone sumoylation negatively regulates transcription in S. cerevisiae. We show that all four core histones are sumoylated and identify specific sites of sumoylation in histones H2A, H2B, and H4. We demonstrate that histone sumoylation sites are involved directly in transcriptional repression. Further, while histone sumoylation occurs at all loci tested throughout the genome, slightly higher levels occur proximal to telomeres. We observe a dynamic interplay between histone sumoylation and either acetylation or ubiquitylation, where sumoylation serves as a potential block to these activating modifications. These results indicate that sumoylation is the first negative histone modification to be identified in S. cerevisiae and further suggest that sumoylation may serve as a general dynamic mark to oppose transcription.

Acetylation↗
PubMed2006

Sumoylation of the yeast Gcn5 protein.

Sumoylation, the process by which the ubiquitin-related SUMO protein is covalently attached to lysine side chains in other proteins, is involved in numerous processes in the eukaryotic cell, including transcriptional repression. In this study, we identify Gcn5, the histone-modifying subunit of the transcriptional regulatory complex SAGA, as a sumoylation substrate in yeast. In vitro, multiple sumoylation of recombinant Gcn5 alone or as a trimer with its interacting proteins Ada2 and Ada3 did not affect Gcn5's histone acetyltransferase (HAT) activity, suggesting that modification of Gcn5 with yeast SUMO (Smt3) may not directly regulate its HAT function. Through site-directed mutagenesis, the primary in vivo sumoylation site was identified as lysine-25, although an unsumoylatable K-to-R mutation of this residue led to no obvious in vivo effects. However, fusion of SUMO to the N-terminus of Gcn5 to mimic constitutive sumoylation resulted in defective growth on 3-aminotriazole media and reduced basal and activated transcription of the SAGA-dependent gene TRP3. Taken together with recent identification of multiple additional subunits of SAGA as sumoylated proteins in vivo, these data suggest that Gcn5 sumoylation may have an inhibitory role in transcriptional regulation.

Binding Sites↗
PubMed2005

Small ubiquitin-like modifying protein isopeptidase assay based on poliovirus RNA polymerase activity.

The ubiquitin-proteasome pathway is the major nonlysosomal proteolytic system in eukaryotic cells responsible for regulating the level of many key regulatory molecules within the cells. Modification of cellular proteins by ubiquitin and ubiquitin-like proteins, such as small ubiquitin-like modifying protein (SUMO), plays an essential role in a number of biological schemes, and ubiquitin pathway enzymes have become important therapeutic targets. Ubiquitination is a dynamic reversible process; a multitude of ubiquitin ligases and deubiquitinases (DUBs) are responsible for the wide-ranging influence of this pathway as well as its selectivity. The DUB enzymes serve to maintain adequate pools of free ubiquitin and regulate the ubiquitination status of cellular proteins. Using SUMO fusions, a novel assay system, based on poliovirus RNA-dependent RNA polymerase activity, is described here. The method simplifies the isopeptidase assay and facilitates high-throughput analysis of these enzymes. The principle of the assay is the dependence of the viral polymerase on a free N terminus for activity; accordingly, the polymerase is inactive when fused at its N terminus to SUMO or any other ubiquitin-like protein. The assay is sensitive, reproducible, and adaptable to a high-throughput format for use in screens for inhibitors/activators of clinically relevant SUMO proteases and deubiquitinases.

Carbon-Nitrogen Lyases↗
PubMed2005

Expression and purification of SARS coronavirus proteins using SUMO-fusions.

Severe acute respiratory syndrome coronavirus (SARS-CoV) proteins belong to a large group of proteins that is difficult to express in traditional expression systems. The ability to express and purify SARS-CoV proteins in large quantities is critical for basic research and for development of pharmaceutical agents. The work reported here demonstrates: (1) fusion of SUMO (small ubiquitin-related modifier), a 100 amino acid polypeptide, to the N-termini of SARS-CoV proteins dramatically enhances expression in Escherichia coli cells and (2) 6x His-tagged SUMO-fusions facilitate rapid purification of the viral proteins on a large scale. We have exploited the natural chaperoning properties of SUMO to develop an expression system suitable for proteins that cannot be expressed by traditional methodologies. A unique feature of the system is the SUMO tag, which enhances expression, facilitates purification, and can be efficiently cleaved by a SUMO-specific protease to generate native protein with a desired N-terminus. We have purified various SARS-CoV proteins under either native or denaturing conditions. These purified proteins have been used to generate highly specific polyclonal antibodies. Our study suggests that the SUMO-fusion technology will be useful for enhancing expression and purification of the viral proteins for structural and functional studies as well as for therapeutic uses.

Coronavirus 3C Proteases↗
PubMed2002

SALSA, a variant of yeast SAGA, contains truncated Spt7, which correlates with activated transcription.

Spt-Ada-Gcn5 acetyltransferase (SAGA) is a previously described histone acetyltransferase/transcriptional coactivator complex in yeast. At promoters of certain genes (HIS3 and TRP3), SAGA has an inhibitory function involving a nonproductive TATA-binding protein interaction mediated by the Spt3 and Spt8 subunits. Related to this, Spt8-less SAGA is a major form of the complex under activating conditions for these genes. In the present study, we purify this activation-specific complex, called SALSA (SAGA altered, Spt8 absent). Besides lacking Spt8, SALSA contains Spt7 subunit that is truncated. Examining the role of this subunit, we find that C-terminally truncated SPT7 resulted in derepressed HIS3 transcription. Furthermore, when grown in rich media (repressing conditions), wild-type cells yielded predominantly SAGA, but Spt7 C-terminal truncations resulted primarily in a form of complex similar to SALSA. Thus, SALSA-like structure and activating function can be partially recapitulated in yeast by truncating the C terminus of Spt7. Overall, these results lead to a model that for a subset of promoters SAGA is inhibitory through Spt3, Spt8, and an Spt8-interacting subdomain of Spt7, whereas SALSA is a form of complex for positive transcriptional regulation. These data clarify a mechanism by which a transcriptional regulatory complex can switch between positive and negative modulation.

Amino Acid Sequence↗
PubMed2002

The SANT domain of Ada2 is required for normal acetylation of histones by the yeast SAGA complex.

Transcription is regulated through chromatin remodeling and histone modification, mediated by large protein complexes. Histone and nucleosome interaction has been shown to be mediated by specific chromatin domains called bromodomains and chromodomains. Here we provide evidence for a similar function of two additional domains within the yeast SAGA complex, containing the histone acetyltransferase Gcn5. We have analyzed deletion and substitution mutations within Gcn5 and Ada2, an interacting protein within SAGA, and have identified substrate recognition functions within the SANT domain of Ada2 and regions of the histone acetyltransferase domain of Gcn5 that are distinct from catalytic function itself. These results suggest that histone and nucleosomal substrate recognition by SAGA involves multiple conserved domains and proteins, beyond those that have been previously identified.

Acetyltransferases↗