Figure 2.

Structural phenotypes of hsp82 alleles and suppressor screen strategy. (A) Chromatin structure of the wild type and mutant hsp82 promoter. At the wild-type allele, HSF occupies HSE1 prior to heat shock, and all three HSEs following it. Its promoter nucleosomes are highly remodeled (DNase I hypersensitive) under non-heat-shock conditions and displaced, along with ORF nucleosomes, upon heat shock (depicted) (Zhao et al. 2005). At the hsp82-ΔHSE1 allele, HSF occupancy is reduced 20-fold relative to HSP82⁺ and its promoter nucleosomes (shaded green) are stable and precisely positioned. They are not detectably altered by heat shock. Nucleosome +1, located downstream of the initiation site, is also detectable at HSP82⁺ under noninducing conditions. (B) Selection/screen strategy employed in this study. Depicted are the three hsp82 alleles (all chromosomal integrants) present in strain HS1004 and the primary phenotypes of the parental strain and suppressor mutants.