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J. Biol. Chem., Vol. 279, Issue 5, 3348-3353, January 30, 2004

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Role of His-16 in Turnover of T4 Pyrimidine Dimer Glycosylase^*

Michael G. Meador, Lavanya Rajagopalan, R. Stephen Lloyd, and M. L. Dodson

From the Sealy Center for Molecular Science and Department of Human Biological Chemistry and Genetics, The University of Texas Medical Branch, Galveston, Texas 77555-1071

Previously, the histidine residue at position 16 in the mature T4 pyrimidine dimer glycosylase (T4-PDG) protein has been suggested to be involved in general (non-target) DNA binding. This interpretation is likely correct, but, in and of itself, cannot account for the most dramatic phenotype of mutants at this position: their inability to restore ultraviolet light resistance to a DNA repair-deficient Escherichia coli strain. Accordingly, this residue has been mutated to serine, glutamic, aspartic acid, lysine, cysteine, and alanine. The mutant proteins were expressed, purified, and their abilities to carry out several functions of T4-PDG were assessed. The mutant proteins were able to perform most functions tested in vitro, albeit at reduced rates compared with the wild type protein. The most likely explanation for the biochemical phenotypes of the mutants is that the histidine residue is required for rapid turnover of the enzyme. This role is interpreted and discussed in the context of a reaction mechanism able to account for the complete spectrum of products generated by T4-PDG during a single turnover cycle.

Received for publication, May 6, 2003 , and in revised form, November 7, 2003.

^* This work was supported in part by National Institutes of Health Grants R01ES04091 and P30ES06676 and NASA/NCI National Institutes of Health Grant NAS2-02059. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Holds the Mary Gibbs Jones Distinguished Chair in Environmental Toxicology. Present address: Center for Research in Occupational and Environmental Toxicology, Oregon Health & Sciences University, Portland, OR 97239-3098.

To whom correspondence should be addressed. Tel.: 409-772-2178; Fax: 409-772-1790; E-mail: bdodson{at}scms.utmb.edu.

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