The helicases DinG, Rep and UvrD cooperate to promote replication across transcription units in vivo

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Abstract
How living cells deal with head‐on collisions of the replication and transcription complexes has been debated for a long time. Even in the widely studied model bacteria Escherichia coli, the enzymes that take care of such collisions are still unknown. We report here that in vivo , the DinG, Rep and UvrD helicases are essential for efficient replication across highly transcribed regions. We show that when rRNA operons ( rrn ) are inverted to face replication, the viability of the dinG mutant is affected and over‐expression of RNase H rescues the growth defect, showing that DinG acts in vivo to remove R‐loops. In addition, DinG, Rep and UvrD exert a common function, which requires the presence of two of these three helicases. After replication blockage by an inverted rrn , Rep in conjunction with DinG or UvrD removes RNA polymerase, a task that is fulfilled in its absence by the SOS‐induced DinG and UvrD helicases. Finally, Rep and UvrD also act at inverted sequences other than rrn , and promote replication through highly transcribed regions in wild‐type E. coli .