RNA polymerase II terminates transcription in vitro in the SV40 origin region

To begin to study signals on DNA that can cause mammalian RNA polymerase II to terminate transcription, we examined the RNA transcripts produced from a number of different DNA templates in a HeLa whole-cell extract. When transcripts initiating from the strong adenovirus late promoter and extending through the SV40 promoter-replication origin region were analyzed, it was observed that a significant fraction (approximately 75%) were terminated within these SV40 sequences. These transcripts, the 3' ends of which were mapped to several sites within an approximately 200 base pair region, appeared to result from transcription termination, as judged by kinetic and pulse-chase experiments. The possible significance of these findings with respect to SV40 gene expression in particular and transcription termination in general are discussed.