DNA polymerase mu (Pol mu), homologous to TdT, could act as a DNA mutator in eukaryotic cells |
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| Authors: | Domínguez O Ruiz J F Laín de Lera T García-Díaz M González M A Kirchhoff T Martínez-A C Bernad A Blanco L |
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| Affiliation: | Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Centro Nacional de Biotecnología (CSIC), Universidad Autónoma, 28049 Madrid, Spain. |
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| Abstract: | A novel DNA polymerase has been identified in human cells. Human DNA polymerase mu (Pol mu), consisting of 494 amino acids, has 41% identity to terminal deoxynucleotidyltransferase (TdT). Human Pol mu, overproduced in Escherichia coli in a soluble form and purified to homogeneity, displays intrinsic terminal deoxynucleotidyltransferase activity and a strong preference for activating Mn(2+) ions. Interestingly, unlike TdT, the catalytic efficiency of polymerization carried out by Pol mu was enhanced by the presence of a template strand. Using activating Mg(2+) ions, template-enhanced polymerization was also template-directed, leading to the preferred insertion of complementary nucleotides, although with low discrimination values. In the presence of Mn(2+) ions, template-enhanced polymerization produced a random insertion of nucleotides. Northern-blotting and in situ analysis showed a preferential expression of Pol mu mRNA in peripheral lymphoid tissues. Moreover, a large proportion of the human expressed sequence tags corresponding to Pol mu, present in the databases, derived from germinal center B cells. Therefore, Pol mu is a good candidate to be the mutator polymerase responsible for somatic hyper- mutation of immunoglobulin genes. |
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