What is it about?
We investigated how the E. coli DNA-copying machinery, the replisome, deals with proteins already bound to the DNA template. Using reconstituted replication assays and bacterial genetics, we found that the helicases Rep and UvrD can help blocked replication forks move past protein-DNA barriers. The strongest in-cell evidence pointed to transcription complexes, the RNA polymerase machinery on DNA, as major natural barriers. Rep stood out because it interacted with DnaB, the main replicative helicase, suggesting that it can act as an additional motor at the fork.
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Why is it important?
The study helps explain how genome duplication can continue in a protein-rich chromosome, where replication forks often meet bound proteins such as RNA polymerase. It supports the idea that accessory helicases may provide an early way to help blocked forks, rather than relying mainly on recombination-based repair. It also shows that similar outcomes can be achieved in different ways: through a fork-associated Rep motor or through the broader activity of UvrD.
Perspectives
We were struck by how well the biochemical and genetic results aligned: helicases that helped blocked replisomes in vitro were also the ones that could support E. coli cells missing Rep and UvrD. A key feature of the paper is the link between Rep and DnaB, which points to Rep acting as a second motor at the replisome rather than just a general DNA-unwinding enzyme. We think the work is useful because it frames protein-bound DNA, especially transcription complexes, as a practical obstacle that cells must deal with during normal chromosome replication.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Rep Provides a Second Motor at the Replisome to Promote Duplication of Protein-Bound DNA, Molecular Cell, November 2009, Elsevier,
DOI: 10.1016/j.molcel.2009.11.009.
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