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Molecular and Cellular Biology, April 2003, p. 2309-2315, Vol. 23, No. 7
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.7.2309-2315.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Polymerase Mu Is a DNA-Directed DNA/RNA Polymerase

Stephanie A. Nick McElhinny1,2 and Dale A. Ramsden1,2,3*

Department of Biochemistry and Biophysics,1 Lineberger Comprehensive Cancer Center,2 Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina3

Received 11 November 2002/ Returned for modification 18 December 2002/ Accepted 8 January 2003

DNA polymerases are defined as such because they use deoxynucleotides instead of ribonucleotides with high specificity. We show here that polymerase mu (pol µ), implicated in the nonhomologous end-joining pathway for repair of DNA double-strand breaks, incorporates both ribonucleotides and deoxynucleotides in a template-directed manner. pol µ has an approximately 1,000-fold-reduced ability to discriminate against ribonucleotides compared to that of the related pol ß, although pol µ's substrate specificity is similar to that of pol ß in most other respects. Moreover, pol µ more frequently incorporates ribonucleotides when presented with nucleotide concentrations that approximate cellular pools. We therefore addressed the impact of ribonucleotide incorporation on the activities of factors required for double-strand break repair by nonhomologous end joining. We determined that the ligase required for this pathway readily joined strand breaks with terminal ribonucleotides. Most significantly, pol µ frequently introduced ribonucleotides into the repair junctions of an in vitro nonhomologous end-joining reaction, an activity that would be expected to have important consequences in the context of cellular double-strand break repair.

* Corresponding author. Mailing address: Room 32-044, Lineberger Comprehensive Cancer Center, Campus Box 7295, Mason Farm Rd., University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295. Phone: (919) 966-9839. Fax: (919) 966-3015. E-mail: Dale_Ramsden{at}med.unc.edu.

Molecular and Cellular Biology, April 2003, p. 2309-2315, Vol. 23, No. 7
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.7.2309-2315.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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