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.