Expression of 93D heat shock puff of Drosophila melanogaster in deficiency genotypes and its influence on activity of the 87C puff

The 93D (hsr-omega) locus of Drosophila: non-coding gene with house-keeping functions

The 93D, or hsr-omega (heat-shock RNA-omega), locus of Drosophila melanogaster and other species of Drosophila, besides being induced as a member of the heat shock gene family, is also selectively and singularly inducible by a variety of agents, notably benzamide, colchicine and vitamin B6 (in species other than D. melanogaster). The genomic structure of this locus is highly conserved in all species, although the primary base sequence has diverged rapidly between species. Three transcripts (two nuclear and one cytoplasmic) are produced by this locus but none of them has any significant protein coding capacity. The profile of the three transcripts varies in a developmental and inducer-specific manner. This locus is developmentally active in nearly all cell types and is essential for viability of flies. Its induction during heat shock is independent of the other members of the heat shock gene family. The other selective inducers act on this locus through separate response elements. hsr-omega activity has a characteristic effect on transcription/turnover of the heat shock induced hsp70 and the alpha-beta transcripts in D. melanogaster. It appears that the hsr-omega locus has important house-keeping functions in transport and turnover of some transcripts and in monitoring the 'health' of the translational machinery of the cell.

Mutations affecting beta-alanine metabolism influence inducibility of the 93D puff by heat shock in Drosophila melanogaster

Effect of mutations at the ebony or black locus on induction of heat shock puffs in polytene nuclei of salivary glands of Drosophila melanogaster larvae were examined by [3H]uridine autoradiography. The levels of beta-alanine in the body are known to be increased by mutation at the ebony locus but decreased by mutation at the black locus. The presence of mutant allele/s at either locus in the homo- or heterozygous condition prevented induction of the 93D puff by heat shock. Elimination of the mutant allele at the ebony or black locus by recombination or by reversion of a P element insertion mutant allele of ebony restored the heat shock inducibility of the 93D puff. In vivo or in vitro administration of excess beta-alanine to salivary glands of wild-type larvae also resulted in the 93D site being refractory to heat shock induction. In agreement with earlier results, non-induction of the 93D puff during heat shock due to the beta-alanine effect was accompanied by unequal puffing of the 87A and 87C loci. The selective inducibility of the 93D puff by benzamide was not affected by ebony or black mutations or by excess beta-alanine in wild-type larvae.