The SV40 72 bp repeat preferentially potentiates transcription starting from proximal natural or substitute promoter elements.

Activation of gene expression by the SV40 72 bp repeat was studied at the transcriptional level by quantitative S1 nuclease mapping of total RNA isolated from Hela cells transfected with chimeric conalbumin promoter-SV40 early gene recombinants. Our results demonstrate that, irrespective of its orientation, the 72 bp repeat is a potentiator of initiation of transcription from "TATA"-box-dependent and -independent "natural" or "substitute" promoter elements. In addition, we show that potential proximal promoter sequences are activated in preference to more distal ones. These results are consistent with the bidirectional entry site model for transcription activation by the 72 bp repeat.