F1 and F2: Two similar genes regulated differently during development of Drosophila melanogaster.

Screening a cDNA library of 2- to 3-day-old flies with poly(A)(+) RNA from male and female flies, we were able to isolate a small number of clones hybridizing preferentially with RNA from female flies. Four cDNA clones, derived from a single mRNA species, proved to be highly abundant in female flies. When we screened a genomic library with the longest cDNA, we obtained two genomic clones, F1 and F2; F1 was a direct copy of the cDNA and F2 was obtained by cross-hybridization. A detailed analysis of these genomic clones revealed two independent genes coding for proteins of 50 kDa that are >90% homologous. RNA analysis with gene-specific probes from the 3' untranslated region showed an expression of F1 in all stages of development with a 5- to 10-fold overexpression of this RNA in female flies compared with males. In contrast to F1, F2 is mainly expressed in late pupae and is expressed only at low levels in adult flies.