September 2, 2015

DNA division can slow to a halt

Single-molecule imaging reveals that DNA replication termination
in E. coli is mediated by kinetic competition between speed of strand
separation by the replisomal helicase and rearrangement of Tus−Ter
interactions during separation of the first six base pairs of Ter.
Multiple termination sites are required to insure fork stoppage. © 2015 KAUST

Termination sites of DNA are shown to stop slow-moving replication forks but not faster ones.

(September 2, 2015)  A key mystery of the DNA replication process has been unraveled by researchers from King Abdullah University of Science and Technology (KAUST).

Before a bacterium can divide, it must make a copy of its genetic material, the circular DNA molecules that resemble bunched rubber bands, through a process called DNA replication. In this process, the two strands of DNA making up the circular DNA molecule unwind and separate to become templates for generating new strands.

To ensure the process is well regulated, the bacterium has set a number of “roadblocks,” or termination sites on the DNA, to ensure the permanent stoppage of  replication forks, Y-shaped structures formed between the strands as the DNA molecule splits.

The Nature study, led by KAUST Ph.D. student Mohamed Elshenawy and Associate Professor Samir Hamdan from KAUST’s Division of Biological and Environmental Science and Engineering, along with colleagues from the University of Wollongong in Australia, showed why termination sites were able to permanently stop replication forks in vitro, while in living bacteria, more than 50 percent of the replication forks that moved towards the termination site continued synthesis without stopping1.

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