Role of Sko1 sumoylation in regulating target site binding

We examine how SUMO post-translational modification of the yeast transcription factor Sko1 affects its binding site selection and affinity. Chromatin immunoprecipitation followed by next-generation sequencing was performed in strains expressing wild-type Sko1 (Sko1-WT) or Sko1 that harbors an Arg-to-Lys mutation at Lys 567 (Sko1-MT), that impairs its sumoylation. We find that, compared with Sko1-WT, SUMO-deficient Sko1 binds numerous additional sites that are near promoters of non-Sko1 target genes. Furthermore, Sko1-MT shows higher occupancy levels than Sko1-WT on most genes that are occupied by both forms. Osmotic stress causes a general rearrangement of Sko1 positions across the genome, but increased numbers of binding sites and occupancy levels are still observed for Sko1-MT after treatment with NaCl. This study indicates that sumoylation attenuates Sko1 association with chromatin and increases its binding specificity. Comparison of binding sites and affinity between wild-type and sumoylation-deficient forms of Sko1.