How RecBCD protects E. coli DNA when copying and transcription collide

What is it about?

We investigated how Escherichia coli cells handle conflicts between DNA replication and transcription when they lack RecBCD, a protein complex involved in processing damaged or stalled DNA structures. We found that head-on encounters between replication forks and highly transcribed ribosomal RNA operons can create severe blocks in cells lacking RecBCD. At these blocked forks, DNA becomes exposed to degradation by nucleases, especially SbcCD. SbcCD also accounts for much of the DNA degradation seen in the normal replication termination area, although degradation there was not fully explained by SbcCD alone and appears to involve additional processes. Together, our results show that RecBCD has important roles both at severe replication-transcription conflicts and during the final stages of chromosome duplication.

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Why is it important?

Accurate chromosome duplication depends not only on starting replication, but also on keeping replication forks moving and finishing replication safely. Our study suggests that RecBCD is especially important when a replication fork is severely blocked by highly active transcription, rather than at every minor conflict. It also helps explain why the termination area of the E. coli chromosome can be vulnerable to DNA loss when RecBCD is absent, while showing that existing models do not yet capture all of the underlying molecular events.

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