In situ quantification of hsp70 and alpha-beta transcripts at 87A and 87C loci in relation tohsr-omega gene activity in polytene cells of Drosophila melanogaster

Abstract

The hsp70-coding duplicate loci at the 87A and 87C sites (the 87C site also carries heat-inducible alpha-beta repeats) in polytene nuclei are known to puff to different levels under conditions in which heat shock does not induce the non-protein-codinghsr-omega gene at the 93D site. To understand the basis of this unequal puffing, the levels of hsp70 and alpha-beta transcripts at the 87A and 87C heat shock loci in polytene chromosomes of Drosophila melanogaster were quantified in situ by hybridization of antisense RNA probes after treatment with heat shock, benzamide, colchicine, heat shock followed by benzamide or heat shock in the presence of colchicine in salivary glands of late third instar larvae. Heat shock, resulting in equal puffing of the 87A and 87C loci, increased the hsp70 transcripts at both sites in proportion to the numbers of hsp70 gene copies at the two loci; levels of alpha-beta transcripts were also elevated at the 87C site following heat shock. Heat shock followed by benzamide treatment, which results in a larger puff at 87A, caused an increase in hsp70 transcripts per gene copy at 87A and a decrease at 87C without any effect on the alpha-beta transcripts; heat shock in the presence of colchicine, which causes the 87C puff to be larger than 87A, resulted in a decrease in hsp70 RNA at 87A but an increase in the levels of hsp70 as well as alpha-beta transcripts at the 87C site. While colchicine treatment enhanced alpha-beta transcripts at the 87C site, without any effect on the hsp 70 transcripts at the 87A or 87C sites, benzamide had no effect on transcripts at either of the sites. The rates of synthesis and turnover of the 87A- and 87C-type hsp70 and of the alpha-beta transcripts differ in spite of their sharing similar 5' upstream regulatory sequences. Metabolism of the different hsr-omega transcripts of the 93D locus seems to influence RNA metabolism at the 87A and 87C sites.