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Journal of Bacteriology, October 2001, p. 6065-6073, Vol. 183, No. 20
Department of Cell and Molecular Biology,
Biomedical Centre, Uppsala University, S-751 24 Uppsala,
Sweden
Received 23 May 2001/Accepted 20 July 2001
The recombinational rescue of chromosome replication was
investigated in Escherichia coli strains with the
unidirectional origin oriR1, from the plasmid R1,
integrated within oriC in clockwise (intR1CW) or counterclockwise
(intR1CC) orientations. Only the intR1CC strain, with replication forks
arrested at the terminus, required RecA for survival. Unlike the
strains with RecA-dependent replication known so far, the
intR1CC strain did not require RecBCD, RecF,
RecG, RecJ, RuvAB, or SOS activation for viability. The overall levels
of degradation of replicating chromosomes caused by inactivation of
RecA were similar in oriC and
intR1CC strains. In the
intR1CC strain, RecA was also needed to
maintain the integrity of the chromosome when the unidirectional
replication forks were blocked at the terminus. This was consistent
with suppression of the RecA dependence of the
intR1CC strain by inactivating Tus, the
protein needed to block replication forks at Ter sites.
Thus, RecA is essential during asymmetric chromosome replication for the stable maintenance of the forks arrested at the terminus and for
their eventual passage across the termination barrier(s) independently of the SOS and some of the major recombination pathways.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.20.6065-6073.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
RecA-Mediated Rescue of Escherichia
coli Strains with Replication Forks Arrested at the
Terminus
*
Corresponding author. Mailing address: Department of
Cell and Molecular Biology, Biomedical Centre, Uppsala
University, Box 596, S-751 24 Uppsala, Sweden. Phone: 46 18 471 4527. Fax: 46 18 53 03 96. E-mail:
santanu.dasgupta{at}icm.uu.se.
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