Single-stranded DNA from oncornavirus-infected cells enriched in virus-specific DNA sequences

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Abstract
A minor fraction of single-stranded DNA (ss-DNA) isolated from native nuclear DNA of normal chicken embryonic cells and cells of other species hybridized with bulk nuclear DNA or cellular RNA in great excess. At least 1/3 of ss-DNA belonging to the nonrepetitious part of the cell genome could be hybridized to homologous RNA. Similar results were obtained with ss-DNA from chicken cells infected by avian myeloblastosis virus (AMV). To investigate whether this enrichment of ss-DNA in transcribed DNA sequences involves provirus DNA, radioactive AMV RNA and c[complementary]DNA copies of AMV RNA were used. Most of the 70S AMV RNA hybridized much faster to ss-DNA from productively infected leukemic cells than to bulk DNA. cDNA, either double-stranded or single-stranded, made in the presence of actinomycin D hybridized to total nuclear DNA with similar kinetics. About half of the double-stranded cDNA molecules hybridized 40-50 times faster to ss-DNA than to total DNA, indicating that only 1 of the provirus DNA strands seems to be present in ss-DNA. This was confirmed by the fact that relatively insignificant amounts of the ss-cDNA molecules made in the presence of actinomycin D could be annealed to ss-DNA as compared with bulk DNA. Apparently, actively transcribed DNA sequences can be selectively distributed in the ss-DNA fraction, probably because of single strand breaks in the vicinity of transcription sites.