REGULATION OF THE GENE SEX-LETHAL - A COMPARATIVE-ANALYSIS OF DROSOPHILA-MELANOGASTER AND DROSOPHILA-SUBOBSCURA

The Drosophila gene Sex-lethal (Sxl) controls the processes of sex det ermination and dosage compensation. A Drosophila subobscura genomic fr agment containing all the exons and the late and early promoters in th e Sri gene of D. melanogaster was isolated. Early Sxl expression in D, subobscura seems to be controlled at the transcriptional level, possi bly by the X:A signal. In the region upstream of the early Sxl transcr iption initiation site are two conserved regions suggested to be invol ved in the early activation of Sxl. Late Sri expression in D. subobscu ra produces four transcripts in adult females and males. In males, the transcripts have an additional exon which contains three translationa l stop codons so that a truncated, presumably nonfunctional Sri protei n is produced. The Sxl pre-mRNA of D. subobscura lacks the poly-U sequ ence presented at the polypirimidine tract of the 3' splice site of th e male-specific exon present in D. melanogaster. Introns 2 and 3 conta in the Sri-binding poly-U stretches, whose localization in intron 2 va ries but in intron 3 is conserved. The Sri protein is fully conserved at the amino acid level in both species.