Characterization of a Yeast Strain that is Deficient in Protein Sumoylation

Sumoylation, the covalent attachment of the SUMO peptide (small ubiquitin-related modifier) to cellular proteins, is a post-translational modification affecting many cellular processes, including transcription. Sumoylated proteins are found specifically on the promoters of transcriptionally active genes. Since the role of SUMO on the promoters for constitutive genes remains largely unknown, we applied the anchor-away technology to generate a yeast strain in which the SUMO conjugating enzyme, Ubc9, could be depleted from nuclei, allowing us to study the effects on transcription. The strain had significantly lower SUMO levels upon rapamycin treatment. However, it also had low levels of basal sumoylation, which reduced further with rapamycin. This rapid disappearance of sumoylated proteins shows that sumoylation is very labile, probably because of the SUMO protease Ulp1s activity. The lower sumoylation in the strain was associated with decreased transcription, reduced RNA Pol II recruitment and lower levels of active histone marks for some genes.