FIGURE 4.

Position at which complexes begin to slip is influenced by DNA sequence and the position of the pol II active site on the DNA. A, CUCU repeat from +2 to +5 is required to observe transcript slippage. The sequences of the expected 7-nt products produced from the +3C/+8G and +8G templates are indicated. B, initiating transcription at –1 rather than +1 changes the sizes of slipped products, but it does not alleviate slipping. Transcription on the +6G template was initiated at +1 with ApC or at –1 with CpA.