Nucleotide sequence analysis of the Drosophila small heat shock gene cluster at locus 67B

Abstract

The four small heat shock protein genes of Drosophila melanogaster clustered at cytological locus 67B have been characterized by DNA sequencing. Over 6250 nucleotides, covering the 5', protein-coding and 3' regions of these genes have been determined together with their predicted amino acid sequences. Each gene possesses characteristic eukaryotic 5' and 3' sequence elements and a single uninterrupted protein-coding region. The four encoded polypeptides of 19,700, 20,600, 23,000 and 23,600 Mr share a homologous stretch of 108 amino acid residues, representing 51 to 62% of their lengths. This region is flanked by sequences of dissimilar length and amino acid composition, located mainly at the amino-terminal end, but also at the extreme carboxyl termini of these proteins. The first 14 amino acids exhibit a small degree of homology, both amongst themselves and with some signal peptides and a transmembrane protein. Investigation of the hydrophilic/hydrophobic characteristics of the four polypeptides revealed, within the conserved 108 amino acid stretch, the presence of an alpha-helical region of very prominent local hydrophilicity, which probably represents a surface structural domain common to each protein. Sequence analysis with respect to transcription initiation and termination and possible regulatory signals is discussed together with some structural predictions for the four proteins.