CHROMATIN STRUCTURE MODULATION IN SACCHAROMYCES-CEREVISIAE BY CENTROMERE AND PROMOTER FACTOR 1

CPF1 is an abundant basic helix-loop-helix-ZIP protein that binds to t he CDEI motif in Saccharomyces cerevisiae centromeres and in the promo ters of numerous genes, including those encoding enzymes of the methio nine biosynthetic pathway. Strains lacking CPF1 are methionine auxotro phs, and it has been proposed that CPF1 might positively influence tra nscription at the MET25 and MET16 genes by modulating promoter chromat in structure. We test this hypothesis and show that the regions surrou nding the CDEI motifs in the MET25 and MET16 promoters are maintained in a nucleosome-free state and that this requires the entire CPF1 prot ein. However, the chromatin structure around the CDEI motifs does not change on derepression of transcription and does not correlate with th e methionine phenotype of the cell. An intact CDEI motif but not CPF1 is required for transcriptional activation from a region of the MET25 upstream activation sequence. Our results suggest that CPF1 functions to modulate chromatin structure around the CDEI motif but that these c hanges at the MET25 and MET16 promoters do not explain how CPF1 functi ons to maintain methionine-independent growth. The presence of CPF1-de pendent chromatin structures at these promoters leads to a weak repres sion of transcription.