Fig. 2.

DNA substrates for RNAP transcription. The linear Xts and Xnts DNA templates contain dG, M₁dG, or PdG (X) either in the transcribed or nontranscribed strands, respectively, downstream of promoters for T7RNAP (T7P) and RNAPII (AdMLP) transcription. Numbers in parentheses indicate positions in the nontranscribed strand of the DNA plasmid construct. Transcription starts at each promoter (+1) and proceeds in the direction of the bent arrows. Transcripts from the T7 promoter incorporate [α-³²P]GTP and from AdMLP incorporate [α-³²P]CTP within the labeling cassette. Stalled complexes restart at the end of the cassette (+5 from the T7 promoter and +15 from AdMLP). Transcript lengths expected from runoff (RO) or from arrest at the X are depicted by lines below each template. The XhoI-BamHI 34-bp sequence inserted in the plasmid construct as described in Materials and Methods is shown with the 18-base primer sequence in an enlarged type size.