POLXc

DNA polymerase X family
POLXc
SMART accession number:SM00483
Description: includes vertebrate polymerase beta and terminal deoxynucleotidyltransferases
Interpro abstract (IPR002054):

DNA carries the biological information that instructs cells how to exist in an ordered fashion: accurate replication is thus one of the most important events in the cell life cycle. This function is mediated by DNA-directed DNA-polymerases, which add nucleotide triphosphate (dNTP) residues to the 5'-end of the growing DNA chain, using a complementary DNA as template. Small RNA molecules are generally used as primers for chain elongation, although terminal proteins may also be used. Three motifs, A, B and C [(PUBMED:2196557)], are seen to be conserved across all DNA-polymerases, with motifs A and C also seen in RNA- polymerases. They are centred on invariant residues, and their structural significance was implied from the Klenow (Escherichia coli) structure: motif A contains a strictly-conserved aspartate at the junction of a beta-strand and an alpha-helix; motif B contains an alpha-helix with positive charges; and motif C has a doublet of negative charges, located in a beta-turn-beta secondary structure [(PUBMED:2196557)].

DNA polymerases (EC 2.7.7.7) can be classified, on the basis of sequence similarity [(PUBMED:3479792), (PUBMED:2196557)], into at least four different groups: A, B, C and X. Members of family X are small (about 40 kDa) compared with other polymerases and encompass two distinct polymerase enzymes that have similar functionality: vertebrate polymerase beta (same as yeast pol 4), and terminal deoxynucleotidyl-transferase (TdT) (EC 2.7.7.31). The former functions in DNA repair, while the latter terminally adds single nucleotides to polydeoxynucleotide chains. Both enzymes catalyse addition of nucleotides in a distributive manner, i.e. they dissociate from the template-primer after addition of each nucleotide. DNA-polymerases show a degree of structural similarity with RNA-polymerases.

This domain is found either at the extreme N or C termini of DNA polymerase X proteins.

GO function:DNA-directed DNA polymerase activity (GO:0003887), DNA binding (GO:0003677)
Family alignment:
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There are 1753 POLXc domains in 1745 proteins in SMART's nrdb database.

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