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.