Two clusters of genes for major chorion proteins of Drosophila melanogaster

cDNA clones complementary to poly(A)-containing RNA from ovarian follicle cells of Drosophila have been prepared. On the basis of restriction mapping and cross hybridization tests, 22 such clones were found to comprise four classes (group I-group IV). Filter-bound DNA from clones in each group hybridized, under stringent conditions, with a single size class of ovarian poly(A)-containing RNA. The mobilities of these RNAs on gels corresponded to those of putative chorion messenger RNAs (Spradling and Mahowald 1979). Translation of the RNAs in vitro yielded proteins with apparent molecular weights 1000-3000 daltons greater than those of mature chorion proteins isolated from purified eggshells. When a membrane fraction from dog pancreas was included in the in vitro translation reaction, the mobilities of the products were indistinguishable from those of major chorion proteins in three cases: c38 (group I), c36 (group II) and c18 (group III). The 16K product of hybrid-selected RNA from group IV clones could not be associated unambiguously with a specific chorion protein. Hybridization of cloned cDNAs to restriction digests of DNA prepared from embryonic nuclei was consistent with the presence of one (c38 and c36) or several (c18) copies of these genes per haploid genome. Hybridization in situ of RNA transcripts from the clones to polytene chromosomes demonstrated that the genes for these four proteins are clustered at two sites. In agreement with previous results (Spradling, Waring and Mahowald 1979), both c36 and c38 are coded at 7E11-7F1-2 on the X chromosome. Group III and group IV clones were both localized at a site on the third chromosome (66D15).