What is it about?
We investigated how Escherichia coli uses accessory helicases to keep chromosome replication moving when the DNA-copying machinery encounters proteins bound to DNA. We compared three candidate helper helicases, Rep, UvrD and DinG, and found that only loss of Rep clearly lengthened the time needed to duplicate the chromosome. We also found that Rep needs its physical interaction with DnaB, a core part of the replication machinery, to support rapid genome duplication. When this Rep–DnaB interaction was disrupted, cells showed signs of increased replication blockage, especially from transcription-related obstacles, and depended more on pathways that process and restart blocked replication forks.
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Why is it important?
DNA replication has to work through a crowded chromosome, not a clean DNA template, so protein-bound DNA can create real barriers to genome duplication. Our results suggest that E. coli reduces these problems by placing Rep at the replisome, where it can act as an accessory motor at the replication fork. This helps explain why the localisation of a DNA helicase may be important for efficient chromosome duplication and for limiting the need for repair-associated restart.
Perspectives
What stands out to us is that Rep activity alone was not enough; Rep had to be brought to the right place through its interaction with DnaB. The C-terminally altered Rep protein could still be present, but without this interaction the chromosome was duplicated much more slowly. We were also struck that the Rep–DnaB interaction did not appear to make the replisome itself faster; rather, it helped position the accessory helicase where it was needed. This gives a clearer view of Rep as a targeted helper motor that supports efficient DNA replication in E. coli.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Localization of an accessory helicase at the replisome is critical in sustaining efficient genome duplication, Nucleic Acids Research, October 2010, Oxford University Press (OUP),
DOI: 10.1093/nar/gkq889.
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