Evidence that TUP1/SSN6 has a positive effect on the activity of the yeast activator HAP1.

The activity of the yeast transcriptional activator HAP1 is controlled by heme and the heme effect is mediated through the heme domain of HAP1. In this report, we show that HAP1 activity is significantly reduced in strains deleted of TUP1 or SSN6, and addition of a heme analog does not allow HAP1 to regain its full activity. Deletion of the heme domain alleviates the requirement for TUP1/SSN6. The results suggest that TUP1/SSN6 have a positive effect on the activity of HAP1 and this effect is mediated through the heme domain. Although TUP1/SSN6 generally repress transcription of many genes, our data indicate they may have positive effect on the expression of certain genes.