EVIDENCE OF AN OVERLAP BETWEEN THE 2 HALF-SITES OF UAS1-B CYC1 - A NEW MODEL FOR CYP1P (HAP1P) DNA-BINDING/

Cyp1p (Hap1p) is a yeast transcriptional regulator belonging to the zi nc-cluster family. CGGNNNTANCGG was identified by PCR selection as the DNA sequence allowing its optimal binding. Nevertheless, this sequenc e is not a consensus sequence, the simultaneous presence of the two CG Gs and the TA generally not being found in the known natural Cyp1p tar gets. In fact, our previous studies showed that the mechanism of Cyp1p DNA binding was target dependent. Data concerning the binding of Cyp1 p to the UAS1-B/CYC1 are presented here. This target, containing the C GGGGTTTACGG sequence, was found to present the particular ability of s tabilizing the binding of only one molecule of some monomeric Cyp1p fr agments. This property was used to investigate the actual contribution of the TT and CGG sequences in the binding of Cyp1p. Our results indi cate that each CGG belongs to a different half-site and, in contrast t o a previous hypothesis, that the T nucleotide located four bases down stream from the left CGG is essential for the binding of one monomer t o each half-site. The two half-sites of the UAS1-B/CYC1 thus overlap.