Alterations in the interaction between GAL4 and GAL80 effect regulation of the yeast GAL regulon mediated by the F box protein Dsg1.

The interplay between the yeast prototypical transcriptional activator Gal4p and the inhibitor protein Gal80p determines the transcriptional status of the genes needed for galactose utilization in Saccharomyces cerevisiae. In this study, we showed that deletion of dsg1 coding for the F box protein Dsg1/Mdm30 delayed but did not eliminate growth of yeast on galactose. Correspondingly, the impaired expression of a GAL1-LacZ reporter in the absence of Dsg1 was only apparent during an early stage of induction. The requirement for Dsg1 in induction was abrogated by the absence of Gal80p or partly bypassed by Gal4 derivatives with decreased interaction with Gal80p. A K23R mutation in the DNA-binding domain of Gal4p was also identified to alleviate the induction defect by dsg1 deletion. On the other hand, the overall accumulation of multi-ubiquitylated Gal4p was not affected by the absence of dsg1 and the induction defect with deletion of dsg1 was partly rescued by disruption of dnm1, a gene encoding a component of the mitochondria division machinery. Taken together, these results suggest that the Dsg1-mediated efficient transcription process of GAL genes may depend on the interaction status between Gal4p and Gal80p.