Figure 5. Dual pathways for σ70 to associate with the TEC in vivo.
(A). Cis-acting pathway (Deighan et al., 2011). The retention in the TEC of the σ70 that was used during initiation enables pausing at transcribed-region −10-like elements on transcription units that are expressed under the control of σ70-dependent promoters. Presence of an initial-transcribed-region σ70-dependent −10-like element increases the σ70 content of downstream TECs and increases the efficiency of pausing at a second σ70-dependent pause element further downstream. Promoter, grey rectangle; σ70-dependent pause elements, black rectangles; RNA, wavy red line. (B). Trans-acting pathway. Binding of σ70 to TECs that have lost the σ factor used during initiation (here, σ28) increases the efficiency of pausing at a transcribed-region σ70-dependent pause element. Promoter, blue rectangle; σ70-dependent pause element, black rectangle; RNA, wavy red line.