[Combined effect of heat shock and ecdysone on the transcription of Drosophila melanogaster polytene chromosomes].

The combined action of ecdysone and temperature elevation (heat shock) on D. melanogaster polytene chromosome transcription has been investigated. It was shown that heat shock while blocking the transcription in ecdysone--induced puffs is not effective in decreasing their size. Thus we are able to observe chromatin decondensation without transcription. The indirect immunofluorescence using an antiserum directed against DNA/RNA hybrids revealed an intense fluorescence in the polytene chromosomes of heat shocked larvae both in the actively transcribed heat shock puffs and in ecdysone stimulated "primary puffs" with blocked transcription. Ecdysone introduced into the media during heat shock is unable to induce any puffs. On the other hand the hormone introduced into the media after temperature elevation (30' of heat shock + 1 hour of ecdysone stimulation) induces some of the "primary puffs". A new approach for cloning the genes inducible by ecdysone and other inducible loci as well has been developed using the data obtained.