Genomic organization of the 87A7 and 87C1 heat-induced loci of Drosophila melanogaster

Abstract The major 70,000 M r heat-induced protein (hsp70) is encoded at two loci in Drosophila melanogaster , 87A7 and 87C1. We have analysed DNA lacking one or other locus to determine the genomic organization of hsp70-coding sequences at the two loci. The 87A7 locus has two hsp70 genes in a divergent orientation, about 1700 base-pairs apart. We have orientated the restriction map of 87A7 onto the polytene chromosome using Df (3 R ) kar D 1 , a deficiency that encodes a shorter 40,000 M r heat-induced protein (hsp40) derived from hsp70. kar D 1 has an altered hsp70 gene in which the 3′-half is deleted and hsp40 is presumably encoded by this deleted distal gene. As kar D 1 makes both hsp70 and hsp40, both genes at 87A7 are active after heat shock and must be transcribed from opposite DNA strands. The 87C1 locus is very large, containing an isolated hsp70 gene separated from two tandem hsp70 genes by a region of about 38,000 base-pairs in which lie the heat-induced αβ transcripts (Lis et al. , 1978). The variable organization of the hsp70 loci is discussed.