Transcription pattern of in vivo-labeled late simian virus 40 RNA: equimolar transcription beyond the mRNA 3' terminus.

We have examined the pattern of RNA transcription on the L (late) DNA strand late in the simian virus 40 virus infectious cycle by separating pulse-labeled RNA chains according to size and hybridizing to an ordered series of DNA fragments obtained by restriction enzyme digestion. From this analysis, the 5' end of the nascent transcript occurs a short distance counterclockwise from 0.735. Transcription proceeds in a clockwise direction. There is equimolar transcription for at least 1,000 nucleotides beyond the 3' end of the mRNA (0.175). The 3' terminus for the largest molecules is in 0.43--0.655. Molecules which represent more than one circuit of the genome are not more than 1% of the total population of nascent molecules. Implications of these findings for models of the biogenesis of mRNA are discussed.