TRANSCRIPTION OF HEAT-SHOCK GENE LOCI VERSUS NON-HEAT SHOCK LOCI IN CHIRONOMUS POLYTENE CHROMOSOMES - EVIDENCE FOR HEAT-INDUCED FORMATION OF NOVEL PUTATIVE RIBONUCLEOPROTEIN-PARTICLES (HSRNPS) IN THE MAJOR HEAT-SHOCK PUFFS

The heat shock response of Chironomus polytene chromosomes was reexami ned. The in vivo effects of heat shock on chromosomal [H-3]uridine lab eling, RNA polymerase II distribution and ribonucleoprotein (RNP) form ation were investigated. One primary result is a clarification of the number and location of chromosomal sites strongly induced by treatment at 37 degrees C for 60 min. In total, seven major heat shock loci wer e identi fled by transcription autoradiography in Chironomus tentans: I-20A, II-16B, II-10C, II-4B, II-1C, III-12B, and IV-5C. Secondly, com bining immunofluorescence with transcription autoradiography, I find R NA polymerase II occurring after heat shock at multiple chromosomal si tes that were also active under normal conditions (20 degrees C). Furt hermore, the results demonstrate conclusively that the presence of RNA polymerase II at heat shock and non-heat shock loci is generally corr elated with [H-3]uridine labeling during heat shock. These latter resu lts extend and corroborate previous findings. Thirdly, the most striki ng result of this study was revealed in ultrathin sections of puffs by electron microscopy: I discerned a site-specific ultrastructural diff erence in putative RNP particles between heat shock versus non-heat sh ock loci. At least three of the seven induced major heat shock puffs ( I-20A, III-12B, IV-5C) were observed to contain globular particles tha t were different, i.e. significantly larger, 250-1,000 Angstrom in dia meter with a prominent 500-750 Angstrom class, than RNP particles of o ther loci under non-heat shock conditions. These large heat shock puff particles presumably represent nascent or newly synthesized heat shoc k RNA associated with protein(s) to form heat shock RNPs (hsRNPs). Thi s finding suggests the possible involvement of novel RNPs (hsRNPs) in transcriptional regulation or heat shock RNA turnover and may stimulat e further molecular investigations on this subject in both cell physio logical and structural terms. I conclude that the locus-specific putat ive hsRNPs are an intrinsic property of greatly increased heat shock g ene transcription.