Non-inducibility of the 93D heat-shock puff in cold-reared larvae of Drosophila melanogaster

Abstract

We have looked for the inducibility of the 93D and other heat-shock loci in salivary gland polytene nuclei of Drosophila melanogaster larvae grown since hatching at 10° C. Benzamide and colchicine, both specific inducers of the 93D in 20°-24°C reared larvae, either inhibit (at 10° C) or do not affect (at 24° C) 93D activity in cold-reared larvae. A 30-min incubation of cold-reared larval salivary glands at 24°C (warm shock) specifically enhances 93D activity without affecting other heat shock loci. However, heat shock at 37° C fails to induce 93D while 87A and 87C are induced unequally. Sodium cacodylate, an arsenic compound, induces all heat-shock loci except 93D; the 87A and 87C loci are equally active in this case. The non-inducibility of the 93D heat-shock locus in cold-reared larvae by its specific inducers is yet another example of its uniqueness and independent regulation. In view of earlier and present results, the unequal transcriptional activity of the 87A and 87C heat-shock loci after heat shock to cold-reared larval salivary glands appears to be due to inactivity of the 93D heat-shock puff.