The yeast transcriptional regulator Hap1 promotes both transcriptional activation and repression. Previous studies have shown that Hap1 binds to the promoter of its own gene and represses its transcription. In this report, we identified the DNA site that allows Haplbinding with high affinity. This Hap 1 -binding site contains only one CGG triplet and is distinct from the typical Hap 1 -binding upstream activation sequences (UASs) mediating transcriptional activation. Furthermore, at the HAP1 promoter, Ssa is bound to DNA with Hap1, whereas Hsp90 is not bound. Intriguingly, we found that histone deacetylases, including Rpd3, Hda1, Sin3 and Hos1, are not required for the repression of the HAP1 gene by Hap1. Rather, they are required for transcriptional activation of the HAP1 promoter, and this requirement is dependent on the HAP1 basal promoter. These results reveal a complex mechanism of transcriptional regulation at the HAP1 promoter, involving multiple DNA elements and regulatory proteins. (c) 2007 Elsevier Inc. All rights reserved.