Promoter structure. The promoter used in these experiments has two copies of a URS1-containing fragment from the IME2 promoter upstream of the CYC1 promoter (UAS, TATA elements T1 and T2, and mRNA initiation site [bent arrow] indicated), and it drives expression of a LacI-LacZ fusion gene. As described previously, LacZ expression is repressed in a manner dependent on the URS1 elements Ume6, Sin3, and Rpd3 (, ). The region upstream of this promoter contains sequences from the URA3 gene, which serves as the plasmid marker. Shown below the promoter structure are the regions (typically 300 bp, with the upstream and downstream boundaries being defined by a pair of PCR primers) that are analyzed by the chromatin immunoprecipitation procedure. The regions labeled URS1 and LacZ are analyzed in Fig. and , whereas the upstream (U) and downstream (D) regions analyzed in Fig. are defined by the approximate number of base pairs from the center of the URS1 elements to the center of the indicated region.