Figure 3.

Backtracked RNA polymerase can act like a Chi site to reduce resection and promote recombination. A) Chi distribution across the E. coli genome is biased, with more correctly oriented Chi sites toward the origin (OriC), and fewer close to the terminus of replication (Ter). Because of this bias, resection by RecBCD is lower toward OriC compared to downstream of the DNA break site. B) RNAP can act like a Chi site. When RecBCD encounters a Chi site, the probability of RecBCD pausing increases. This pause results in a switch from exonucleolytic activity of RecBCD to the RecA loading activity. Thus, RecBCD loads RecA to allow for recombination at a Chi site. We hypothesize that backtracked RNAP acts analogously, promoting a RecBCD pause and stimulating recombination.