Published online 24 August 2005
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Characterization of SpPol4, a unique X-family DNA polymerase in Schizosaccharomyces pombe
Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma Madrid, Spain
*To whom correspondence should be addressed. Tel: +34 91 497 8493; Fax: +34 91 497 4799; Email: lblanco{at}cbm.uam.es
Received May 25, 2005. Revised August 3, 2005. Accepted August 3, 2005.
As predicted by the amino acid sequence, the purified protein coded by Schizosaccharomyces pombe SPAC2F7.06c is a DNA polymerase (SpPol4) whose biochemical properties resemble those of other X family (PolX) members. Thus, this new PolX is template-dependent, polymerizes in a distributive manner, lacks a detectable 3'
5' proofreading activity and its preferred substrates are small gaps with a 5'-phosphate group. Similarly to Polµ, SpPol4 can incorporate a ribonucleotide (rNTP) into a primer DNA. However, it is not responsible for the 1–2 rNTPs proposed to be present at the mating-type locus and those necessary for mating-type switching. Unlike Polµ, SpPol4 lacks terminal deoxynucleotidyltransferase activity and realigns the primer terminus to alternative template bases only under certain sequence contexts and, therefore, it is less error-prone than Polµ. Nonetheless, the biochemical properties of this gap-filling DNA polymerase are suitable for a possible role of SpPol4 in non-homologous end-joining. Unexpectedly based on sequence analysis, SpPol4 has deoxyribose phosphate lyase activity like Polß and Pol
, and unlike Polµ, suggesting also a role of this enzyme in base excision repair. Therefore, SpPol4 is a unique enzyme whose enzymatic properties are hybrid of those described for mammalian Polß, Pol and Polµ.
Present address: José F. Ruiz, Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Spain
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