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 cerevisiae FBP1 gene, which codes for fructose-1,6-bisphosphatase. A strong, constitutive, DNase I, micrococcal nuclease and S1 nuclease hypersensitive site is present close to the 3' end of the coding region. In the repressed state, positioned nucleosomes exist around this site, and subtle changes occur in this nucleosomal organization upon derepression. A DNase I hypersensitive region is located within the promoter between positions -540 and -400 and its extends towards the gene in the derepressed state, leading to an alteration of nucleosomal positioning. Psoralen crosslinking of chromatin, which is used for the first time to study the mobility of restriction fragments from an RNA polymerase II gene, revealed that part of the promoter is nucleosome-free, in accordance with the results of DNase I digestion. A model is presented that, based on the chromatin structure, puts forward the hypothesis that the promoter UAS is located between -540 and -340. Finally, psoralen crosslinking, as well as digestions with micrococcal nuclease or restriction endonucleases suggests that most if not all of the copies of the active FBP1 gene are covered by nucleosomes.