At least one essential function of Smt3p, a Saccharomyces cerevisiae ubiquitin-like protein similar to the mammalian protein SUMO-1, involves its posttranslational covalent attachment to other proteins. Using Smt3p affinity chromatography, we have isolated the second enzyme of the Smt3p conjugation pathway and have found that it is identical to Ubc9p, a previously identified protein that has extensive sequence similarity to the ubiquitin-conjugating enzymes (E2s) and that is required for yeast to progress through mitosis. A hallmark of E2s is the ability to form a thioester bond-containing covalent intermediate with ubiquitin (Ub). While we were unable to detect formation of a Ub approximately Ubc9p thioester, Ubc9p was found to form a thioester with Smt3p, indicating that Ubc9p is the functional analog of E2s in the Smt3p pathway and that this step is distinct from the ubiquitin pathway. Ubc9p is required for attachment of Smt3p to other proteins in vitro, suggesting that it is the only such enzyme in S. cerevisiae. These results suggest that, like ubiquitination, Smt3p conjugation may be a critical modification in cell cycle regulation.
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Gene/Complex | Qualifier | Gene Ontology Term | Annotation Extension | Evidence | Source | Assigned On |
---|---|---|---|---|---|---|
UBC9 | enables | SUMO transferase activity | IDA | SGD | 2013-08-07 | |
UBC9 | involved in | protein sumoylation | IMP | SGD | 2013-08-07 | |
UBC9 | involved in | protein sumoylation | IDA | SGD | 2013-08-07 |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Interactor | Interactor | Assay | Annotation | Action | Modification | |
---|---|---|---|---|---|---|
Figure 3|ubiquitin transthiolation | UBA1 | PEX4 | Biochemical Activity | manually curated | Bait-Hit | ubiquitinylated lysine |
Figure 3|ubiquitin transthiolation | UBA1 | RAD6 | Biochemical Activity | manually curated | Bait-Hit | ubiquitinylated lysine |
thioester formation on Ubc9; Figure 1 (DTT-sensitive eluate of column pre-loaded with Aos1/Uba1 (E1)) | UBA2 | AOS1 | Reconstituted Complex | manually curated | Hit-Bait | No Modification |
Figure 3|ubiquitin transthiolation | UBC4 | UBA1 | Biochemical Activity | manually curated | Hit-Bait | ubiquitinylated lysine |
thioester formation on the column; Figure 1 (DTT-sensitive eluate of column pre-loaded with Aos1/Uba1 (E1))|thioester formation on the column; Figure2 | UBC9 | UBA2 | Biochemical Activity | manually curated | Hit-Bait | sumoylated lysine |