Figure 4.

Primer extension analysis of bubble transcripts. The primer extension products represent forward transcripts from the wtNT bubble template (lanes 1–4) or the P_hag homoduplex (lane 5) generated by core in the presence of no added σ (−), σ^D, σ^A, or σ^X as indicated (A); forward transcripts from the wtT bubble template generated by core alone (−) or in the presence of σ^X, σ^A, or σ^D (B); and reverse transcripts from the wtT bubble template by core alone (−), or in the presence of σ^X or σ^A as indicated (C). Reference positions are indicated based on comigration of sequencing lanes (A, C, G, T).