Drosophila melanogaster genomic sequences that hybridize with v-myc have been reported (B.-Z. Shilo and R. A. Weinberg, Proc. Natl. Acad. Sci. U.S. A. 78:6789-6792, 1981). We have detected Drosophila RNA sequences that also hybridize with v-myc. In an attempt to characterize these RNA sequences, we used v-myc hybridization probes to isolate Drosophila genomic seg'ments. None Despite the lack of structural homology between the Drosophila and v-myc sequences, the initial results of our investigations into the pattern of expression of the v-mychybridizing RNA species were novel enough to warrant their completion. Polyadenylic acid-containing transcripts complementary to v-myc and to the Drosophila genomic segments have been detected in embryos, pupae, adults, and Kc cells and on polyribosomes in Kc cells, suggesting that the Drosophila genomic sequences exist in the form of functional genes. We have found that certain transcripts are present in preblastoderm embryos and that their levels fall during midembryogenesis and remain low during the 4 days of larval life. These transcripts reappear during metamorphosis and are present in adults at low levels. In adults, the embryo RNA species are detectable only in ovaries. These results indicate that the early embryonic transcripts are of maternal origin and that their expression may play a role in early development. MATERIALS AND METHODSCell and animal culture. The Drosophila Kco cell line (Kc) was maintained on D20 medium (13) (GIBCO Laboratories) containing 5% fetal calf serum (GIBCO Laboratories). Cell lines were maintained in monolayer cultures at 25°C. An Oregon R strain of D. melanogaster was used as the source of RNA for all developmental stages analyzed. The sources of the RNA preparations (see Fig. 6) were as follows. Embryos were from an 18-h nonsynchronized collection. Pupae were collected from the walls of culture bottles at 160 h after egg deposition. Synchronization of the pupae was achieved by limiting the time for egg deposition to 2 h. The age of adult flies used for RNA was not controlled. 7 on May 9, 2018 by guest