Small circular deoxyribonucleic acid of Drosophila melanogaster: homologous transcripts in the nucleus and cytoplasm.

We have recently characterized small circular DNA of Drosophila cultured cells in terms of its average size, sequence complexity, and homology to intermediate repetitive DNA. We show here that transcripts homologous to small circular DNA are present in various RNA fractions. Nuclear poly(A+), nuclear poly(A-), and polysomal poly(A+) RNA drive 10, 7, and 20%, respectively, of in vitro labeled small circular DNA tracer into hybrid. Sequences complementary to small circular DNA are at least 10-fold more concentrated in nuclear poly(A+) RNA than in nuclear poly(A-) or polysomal poly(A+) RNA. We do not detect significant homology between poly(A-) cytoplasmic RNA and small circular DNA. Assuming that only the least complex component of small circular DNA is driven into hybrid and that transcription is asymmetric, we use the results obtained here and previously published data to calculate the sequence complexity and relative concentration of nuclear poly(A+), nuclear poly(A-), and polysomal poly(A+) RNA homologous to small circular DNA.