An unusual split Drosophila heat shock gene expressed during embryogenesis, pupation and in testis.

Gene 2, one of the seven heat shock genes from locus 67B of Drosophila melanogaster, is transcribed into two polyadenylated RNAs having different developmental profiles of expression. The smaller transcript, of about 560 nucleotides, is expressed from mid-embryogenesis to the first two larval stages and again at the beginning of pupation. The larger transcript, 780 nucleotides, contains an additional 5' exon, accounting for its larger size. It is detected in pupae and adults, is male-specific and is localized in the testes. Heat shock does not affect the abundance of these two transcripts but induces the accumulation of a third RNA species of about 2000 nucleotides. This heat-shock RNA has the same cap site as the embryonic transcript, while its 3' portion entirely includes the neighbouring hsp22 gene. It appears, therefore, that in this case, heat shock alters the normal transcription termination process. By contrast to most heat shock genes, gene 2 contains several micro introns. One long open reading frame common to the three transcripts encodes a putative polypeptide of 111 amino acid residues. No homology was found with the other small heat shock genes of locus 67B.