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Journal of Bacteriology, May 1999, p. 2878-2882, Vol. 181, No. 9
Department of Biology, Boston University,
Boston, Massachusetts 02215,1 and School
of Public Health, Boston University School of Medicine, Boston,
Massachusetts 021182
Received 13 July 1998/Accepted 22 February 1999
DNA-DNA interstrand cross-links are the cytotoxic lesions for many
chemotherapeutic agents. A plasmid with a single nitrogen mustard (HN2)
interstrand cross-link (inter-HN2-pTZSV28) was constructed and
transformed into Escherichia coli, and its replication
efficiency (RE = [number of transformants from
inter-HN2-pTZSV28]/[number of transformants from control]) was
determined to be ~0.6. Previous work showed that RE was high because
the cross-link was repaired by a pathway involving nucleotide excision
repair (NER) but not recombination. (In fact, recombination was
precluded because the cells do not receive lesion-free homologous DNA.)
Herein, DNA polymerase II is shown to be in this new pathway, since the
replication efficiency (RE) is higher in a
polB+ (~0.6) than in a
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Copyright © 1999, American Society for Microbiology. All rights reserved.
DNA Polymerase II (polB) Is Involved in
a New DNA Repair Pathway for DNA Interstrand Cross-Links in
Escherichia coli
polB
(~0.1) strain. Complementation with a polB+-containing plasmid restores RE to
wild-type levels, which corroborates this conclusion. In separate
experiments, E. coli was treated with HN2, and the relative
sensitivity to killing was found to be as follows: wild type < polB < recA < polB
recA ~ uvrA. Because cells deficient in either
recombination (recA) or DNA polymerase II
(polB) are hypersensitive to nitrogen mustard killing,
E. coli appears to have two pathways for cross-link repair:
an NER/recombination pathway (which is possible when the cross-links
are formed in cells where recombination can occur because there are
multiple copies of the genome) and an NER/DNA polymerase II pathway.
Furthermore, these results show that some cross-links are uniquely
repaired by each pathway. This represents one of the first clearly
defined pathway in which DNA polymerase II plays a role in E. coli. It remains to be determined why this new pathway prefers
DNA polymerase II and why there are two pathways to repair cross-links.
*
Corresponding author. Mailing address: Department of
Biology, Boston University, Boston, MA 02115. Phone: (617) 353-9259. Fax: (617) 353-6340. E-mail: loechler{at}bu.edu.
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