Our group has continued their studies on the regulation of heat shock gene expression, with emphasis on the structure and function of the heat shock transcription factor (HSF) and on the organization of the heat shock gene promoter in chromatin. The domains of HSF important for regulating the monomer-trimer transition and for transcriptional activity were further defined, and protease mapping of the global physical structure of HSF was initiated. HSF was determined to be phosphorylated, with changes in the phosphorylation pattern observed after heat stress. Flies carrying mutations in the HSF gene were isolated, and the homozygous mutant phenotype was found to be larval lethal, indicating a requirement for HSF function during the normal development of Drosophila. This group has also continued work on the ATP-dependent nucleosome remodeling factor (NURF) discovered in the previous year. In this period, NURF was purified to homogeneity by seven chromatographic steps, and found to consist of 4 subunits. In studies of mitotic chromatin structure, the displacement of a number of transcription factors was observed; displacement occurred on bulk chromatin as well as on the human hsp70 promoter. These results suggest a new window in cell cycle that could be exploited for resetting transcriptional programs.
