Molecular analysis of a gene in a developmentally regulated puff of Drosophila melanogaster.

Abstract

An increase in the concentration of the steroid hormone ecdysone in late larval life triggers a profound change in the pattern of polytene chromosome puffs in the D. melanogaster salivary gland. One of the preexisting puffs that regress as the ecdysone concentration increases is located at the 3C11-12 bands, the site of the Sgs-4 gene which codes for the sgs-4 protein. The sgs-4 protein is one of the proteins in the salivary glue secretion. Cloned segments of chromosomal DNA that define a 60 kilobase region containing the 0.9 kilobase Sgs-4 gene were isolated and the position and orientation of Sgs-4 within this region were determined. Fine structure restriction endonuclease mapping shows that approximately 45% of this gene consists of tandemly repeated sequences of 21 base pairs that occupy most of its 5'' half; most of the amino-terminal half of the sgs-4 protein consists of tandemly repeated amino acid sequences of 7 residues. The amount of Sgs-4 mRNA as a function of developmental stage and in 9 different strains, 4 of which produce little or no sgs-4 protein, is reported. Three of the null strains produce minute amounts of the mRNA and 1 yields none; the 5 sgs-4 producing strains yield abundant amounts. The mRNA from these strains exhibit different lengths, which correlate with different gene lengths that appear to result from different numbers of the repeated sequences in their tandem arrays.