Figure 2.

Transcript slippage by pol II is drastically reduced when the polymerase is halted 10 or more bases downstream of +1. Transcription was carried out on the indicated templates (see Fig. 1) with dinucleotide primers in the absence of GTP as described in Experimental Procedures. RNAs in the indicated lanes were digested with RNase T1. Arrowheads designate the expected G-stop (nonslipped) transcripts. Slippage and leakthrough transcripts are marked by asterisks and pound signs, respectively. The percentage slippage is the fraction of complexes that underwent at least one round of transcript slippage. Lengths of selected RNAs are given in the margins of the gel.