DNA polymerase mu (Pol mu), homologous to TdT, could act as a DNA mutator in eukaryotic cells.
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.
Domínguez
O
O
Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Centro Nacional de Biotecnología (CSIC), Universidad Autónoma, 28049 Madrid, Spain.
Ruiz
J F
JF
Laín de Lera
T
T
García-Díaz
M
M
González
M A
MA
Kirchhoff
T
T
Martínez-A
C
C
Bernad
A
A
Blanco
L
L
D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D002874:Chromosome Mapping; D002897:Chromosomes, Human, Pair 7 / Q000235:genetics; D004247:DNA / Q000235:genetics* / Q000378:metabolism*; D004253:DNA Nucleotidylexotransferase / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D005803:Genes, Immunoglobulin; D006801:Humans; D017403:In Situ Hybridization; D066298:In Vitro Techniques; D008221:Lymphoid Tissue / Q000201:enzymology; D008969:Molecular Sequence Data; D009154:Mutation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D012333:RNA, Messenger; D011994:Recombinant Proteins; D004247:DNA; C407743:DNA polymerase mu; D004253:DNA Nucleotidylexotransferase; D004259:DNA-Directed DNA Polymerase