HSF RECRUITMENT AND LOSS AT MOST DROSOPHILA HEAT-SHOCK LOCI IS COORDINATED AND DEPENDS ON PROXIMAL PROMOTER SEQUENCES

The heat shock response in Drosophila is primarily dependent on the bi nding of the heat shock transcription factor, HSF, to conserved sequen ces in heat shock gene promoters, the heat shock elements (HSEs). Here we examine the kinetic relationship of HSF binding to chromosomal loc i and heat shock gene transcription in vivo. The features of heat shoc k promoters that determine the kinetics of HSF binding are also examin ed. Analyses of HSF association by indirect immunofluorescence with an anti-HSF antibody reveal that fluorescent signals at many loci on pol ytene chromosomes rapidly increase and then gradually decrease as heat shock time progresses. While overall amounts of fluorescent signal va ry from locus to locus, the patterns of acquisition and loss of HSF at most loci are coordinated with only one identified exception. Immunos taining with an anti-RNA polymerase II antibody indicates that the kin etics of RNA polymerase II accumulation on the heat shock loci are sim ilar to those of HSE Furthermore, nuclear run-on assays confirm that t he major heat shock genes are coordinately transcribed during the atte nuation period. In contrast, the kinetics of HSF association with HSE ''polymers'' in a transgenic fly strain are not coordinated with those of endogenous loci. The addition of core promoter sequences to one of the HSEs found in the polymer restores coordinate HSF binding, sugges ting that the kinetic patterns of HSF binding depend on a core promote r located near the HSEs. Finally, the distribution of the heat shock p rotein HSP70 is examined for its role in regulating the attenuated res ponse of HSF to heat shock.