Abstract
Polysomal and postpolysomal mRNAs were prepared from Drosophila egg chambers or embryos of different developmental stages. Cell-free translation of these mRNAs followed by two-dimensional gel electrophoresis of the products indicated the presence of a specific mRNA that appears to be translated (polysome-associated) during oogenesis. This mRNA, designated T1 mRNA, is selectively excluded from polysomes in 3-hr- and 5-hr-old embryos and is again translated in 18-hr-old embryos. A clone containing DNA complementary to T1 mRNA was selected from a library of recombinant DNA prepared from polyadenylylated ovary RNA. This clone was positively identified by hybrid-selected translation followed by two-dimensional gel electrophoresis and autoradiography. T1 mRNA is polyadenylylated and codes for a small, acidic protein. The cloned probe hybridizes to a unique site (2L-39CD) of the polytene chromosomes, very close to the histone genes. The results suggest that this mRNA is under specific translational regulation in contrast to a background of a large number of other abundant mRNAs that are translated at all developmental stages examined.