GAL4 GAL80-DEPENDENT NUCLEOSOME DISRUPTION DEPOSITION ON THE UPSTREAMREGIONS OF THE YEAST GAL1-10 AND GAL80 GENES/

Metabolic reactivation (incubating spheroplasts with galactose and cas amino acids) causes disruption of nucleosomes from the upstream region s of the yeast GAL1, GAL10, and GAL80 genes, The disruption is specifi c. It depends on the transcription activator Gal4; it only occurs in g alactose-reactivated chromatin from galactose-grown cells; it only aff ects upstream region, gene-proximal nucleosomes. Due to this specifici ty and because some of the same regions have shown induction-dependent changes by in vivo analyses, we suggest that the nucleosome-disrupted structure produced by reactivation is the authentic chromatin structu re for these regions under conditions of galactose-induced GALI-10 and GAL80 expression. It is necessary to carry out a spheroplast reactiva tion treatment in order to observe this disrupted structure in nuclear chromatin because nucleosomes are redeposited onto these regions duri ng the preliminary steps of nuclear isolation (cell harvest/ spheropla st preparation) probably in response to the nonphysiological condition s associated with these steps, However, during the same isolation proc edures in cells lacking Gal80 protein, there is no nucleosome depositi on on these regions, and the in vivo disrupted structure remains prese nt in the nuclear chromatin, There fore, the nucleosome deposition pro cess that operates in wild-type cells is dependent on Gal80 protein, d efining another activity of this negative regulator.