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Journal of Bacteriology, May 1999, p. 2878-2882, Vol. 181, No. 9
0021-9193/99/$04.00+0
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

Mark Berardini,1 Patricia L. Foster,2 and Edward L. Loechler1,*

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 Delta 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.

Journal of Bacteriology, May 1999, p. 2878-2882, Vol. 181, No. 9
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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