Chromatin immunoprecipitation assays are used to map H3 and H4 acetylation over the promoter nucleosomes and the coding region of the Saccharomyces cerevisiae SUC2 gene, under repressed and derepressed conditions, using wild type and mutant strains. In wild type cells, a high level of H3 acetylation at the distal end of the promoter drops sharply toward the proximal nucleosome that covers the TATA box, a gradient that become even steeper on derepression. In contrast, substantial H4 acetylation shows no such gradient and extends into the coding region. Overall levels of both H3 and H4 acetylation rise on derepression. Mutation of GCN5 or SNF2 lead to substantially reduced SUC2 expression; in gnc5 there is no reduction in basal H3 acetylation, but large reductions occur on derepression. SNF2 mutation has little effect on H3 acetylation, so SAGA and SWI/SNF recruitment seem to be independent events. H4 acetylation is little affected by either GCN5 or SNF2 mutation. In a double snf2/gcn5 mutant (very low SUC2 expression), H3 acetylation is at the minimal level, but H4 acetylation remains largely unaffected. Transcription is thus linked to H3 but not H4 acetylation. Chromatin immunoprecipitation assays show that Tup1p is evenly distributed over the four promoter nucleosomes in repressed wild type cells but redistributes upstream on derepression, a movement probably linked to its conversion from a repressor to an activator.The Saccharomyces cerevisiae SUC2 gene codes for invertase, an enzyme that catalyzes the hydrolysis of sucrose and raffinose to provide the cell with glucose in the absence of this essential fuel. It has been widely used to study the mechanisms underlying glucose regulation in yeast. Because these mechanisms result in changes in chromatin structure, this has been a long-lasting field of research. We first analyzed the DNase I sensitivity of the SUC2 gene (1) as well as nucleosome positioning under repressing and derepressing conditions, in both wild type cells (2) and in regulatory mutants (3). These initial data, obtained by indirect end labeling, showed that four nucleosomes are positioned on the promoter in such a way that certain crucial elements, including the TATA box, are occluded, whereas other regulatory sequences are nucleosome-free (2). These results were refined by other workers (4, 5) who mapped the four nucleosomes at high resolution by primer extension analysis.The SUC2 gene is repressed in the presence of glucose by the Ssn6-Tup1 corepressor complex (6, 7), which is tethered to the promoter by Mig1p (8). Tup1-mediated repression of SUC2 results in deacetylation of histone H3 at the promoter, as shown by an increase in H3 acetylation in tup1 mutants, but a lack of Tup1p does not change the acetylation level of H4 (9). This result contrasts with findings for other Tup1-regulated genes in which the repression also results in deacetylation of H4 (9).The SUC2 gene is effectively derepressed by lowering the concentration of glucose (10), and several genes required for derepression were ide...