In vitro transcription of the avian oncornavirus genome by the RNA-directed DNA polymerase: effect of actinomycin D on the extent of transcription.

The minus-strand component of double-stranded DNA synthesized by the avian oncornavirus RNA-directed DNA polymerase in vitro represents as much of the nucleotide sequences of the viral genome as single-stranded DNA synthesized in the presence of actinomycin D. Since actinomycin D inhibits doublestranded DNA formation, we propose that the principal effect of the drug on RNA-directed DNA synthesis is the reduction in synthesis of plus-strand DNA, thereby allowing single-stranded minus-strand DNA to accumulate. This effect, rather than increasing the extent of genome transcription, is responsible for the more uniform nature of the DNA transcripts synthesized in the presence of actinomycin D.