CHROMATIN STRUCTURE OF THE YEAST FBP1 GENE - TRANSCRIPTION-DEPENDENT CHANGES IN THE REGULATORY AND CODING REGIONS

We have studied the chromatin structure of the Saccharomyces cerevisia e FBP1 gene, which codes for fructose-1,6-bisphosphatase. A strong, co nstitutive, DNase I, micrococcal nuclease and SI nuclease hypersensiti ve site is present close to the 3' end of the coding region. In the re pressed state, positioned nucleosomes exist around this site, and subt le changes occur in this nucleosomal organization upon derepression. A DNase I hypersensitive region is located within the promoter between positions -540 and -400 and it extends towards the gene in the derepre ssed state, leading to an alteration of nucleosomal positioning. Psora len crosslinking of chromatin, which is used for the first time to stu dy the mobility of restriction fragments from an RNA polymerase II gen e, revealed that part of the promoter is nucleosome-free, in accordanc e with the results of DNase I digestion. A model is presented that, ba sed on the chromatin structure, puts forward the hypothesis that the p romoter UAS is located between -540 and -340. Finally, psoralen crossl inking, as well as digestions with micrococcal nuclease or restriction endonucleases suggests that most if not all of the copies of the acti ve FBP1 gene are covered by nucleosomes.