Isolation of two Drosophila melanogaster genes abundantly expressed in the ovary during vitelline membrane synthesis

Several genomic clones were isolated from a Drosophila library screened with cDNA prepared from abundant adult female mRNA. Cytoplasmic dot hybridizations have shown that the genes in all of these clones are expressed only in posteclosion (stages 8-14) follicles. One set of overlapping clones (lambda 20, lambda 28, and lambda 30) was localized by in situ hybridization to 66D, a previously described locus for chorion genes. Restriction mapping demonstrated that these clones contained chorion genes which had been isolated previously. Another clone, lambda 7, was mapped to chromosomal region 26A. This clone carries genes that hybridized to mRNA species similar or identical in size to the known chorion genes encompassed by lambda 28. Furthermore, one of these genes shows homology to the 66D chorion locus, apparently with the s18-1 gene. R-loop and S1-nuclease mapping indicated that lambda 7 contains two genes of 700-800 base pairs in length. Dot hybridization of cytoplasmic RNA from egg chambers demonstrated that these genes are expressed predominantly during stages 9 + 10, the time of vitelline membrane synthesis. Analysis of DNA extracted from embryos and various female tissues by dot hybridization showed that lambda 7 sequences are not amplified in the mature ovary. These results suggest that the two genes carried by lambda 7 and derived from region 26A may code for protein components of the vitelline membrane. In addition it appears that some evolutionary relatedness exists between one of these genes and a member of the chorion multigene family.