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J. Bacteriol. doi:10.1128/JB.00476-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Role of Escherichia coli DNA Polymerase I in Conferring Viability Upon the dnaN159 Mutant Strain

Department of Biochemistry, School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, 3435 Main Street, 140 Farber Hall, Buffalo, New York 14214

^* To whom correspondence should be addressed. Email: mdsutton{at}buffalo.edu.

	Abstract

The Escherichia coli dnaN159 allele encodes a mutant form of the -sliding clamp (159) that is impaired for interaction with the replicative DNA polymerase (Pol), Pol III. In addition, strains bearing the dnaN159 allele require functional Pol I for viability. We have utilized a combination of genetic and biochemical approaches to characterize the role(s) played by Pol I in the dnaN159 strain. Our findings discussed below indicate that elevated levels of Pol I partially suppress the temperature sensitive growth phenotype of the dnaN159 strain. In addition, we demonstrate that the clamp stimulates processivity of Pol I in vitro, and that 159 is impaired for this activity. The reduced ability of 159 to stimulate Pol I in vitro correlates with our finding that single strand (ss) DNA gap repair is impaired in the dnaN159 strain. Taken together, these results suggest that: (i) the clamp-Pol I interaction may be important for proper Pol I function in vivo; and (ii) in the absence of Pol I, ssDNA gaps may persist in the dnaN159 strain, leading to lethality of the dnaN159 polA strain.