DNA sequence analysis reveals extensive homologies of regions preceding hsp70 and alphabeta heat shock genes in Drosophila melanogaster.

Two kinds of RNA are synthesized at the 87C1 chromosomal locus of Drosophila melanogaster in response to heat shock. One of these codes for the major heat shock protein, hsp70; the other, alphabeta RNA, derives from tandemly repeated alphabeta units consisting of adjacent alpha and beta DNA elements and has no identified translation product. Another DNA element, gamma, flanks the 5' ends of some alphabeta units. Here we report the complete nucleotide sequence of the 617-base-pair alpha and the 733-base-pair gamma element as well as a portion of the longer beta element. Sequence comparisons between the gamma element and the two hsp70 genes at 87C1 reveal that the 406 base pairs of gamma immediately upstream from the 5' end of the alphabeta unit exhibit 97.5% homology with the sequences at and upstream from the 5' end of the hsp70 genes. A similar homology also exists between gamma and an hsp70 gene present at another heat shock locus, 87A7, which contains no alphabeta units. These results, in conjunction with previous observations, strongly suggest that the coordinate induction by heat shock of the hsp70 and alphabeta genes is a consequence of their homologous 5' flanking sequences. We propose that this extraordinary degree of sequence conservation stems from the recent transposition of alphabeta DNA to the 87C1 locus, an event that brought alphabeta sequences adjacent to, and under the regulation of, the hsp70 control element.