Allelic variation at the nucleotide level in Drosophila glue genes

Abstract

We have sequenced a 4.7 kb genomic fragment from the chromosomal region 68C of the Drosophila melanogaster wild-type strain Formosa which contains the salivary gland secretion protein genes sgs3 and sgs7. A comparison of this sequence with that from the same region of Oregon R (Garfinkel et al. 1983) shows that the major difference in this segment is a 300 bp region, corresponding to 20 of the 15 bp tandemly repeated units which compose the central coding region of sgs3 Oregon, which is absent in the Formosa strain. The order of the remaining repeated units, common to the two strains, suggests that this region is relatively stable and does not undergo frequent rearrangements or mutations. The 5′ and 3′ flanking sequences of the transcribed regions, which represent ca. seventy percent of our sequencing data, appear to be as strongly conserved as the transcribed sequences themselves. In the course of in vitro manipulations of the Formosa sequence, we have isolated two spontaneous deletions of repeated units in the coding region of sgs3 and discuss possible mechanisms leading to variation in sgs3 alleles.