| Type: | Family | Name: | DNA nucleotidylexotransferase (TdT) / DNA-directed DNA/RNA polymerase mu |
| Description: | DNA carries the biological information that instructs cells how to exist in an ordered fashion: accurate replication is thus one of the mostimportant 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 forchain elongation, although terminal proteins may also be used. Three motifs, A, B and C [], 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 Klenlow (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 [].DNA polymerases () can be classified, on the basis of sequence similarity [, ], into at least four different groups: A, B, C and X. Members of family X are small (about 40 Kd) compared with other polymerases and encompass two distinct polymerase enzymes that have similar functionality: vertebrate polymerase beta (same as Saccharomyces cerevisiaepol 4), and terminal deoxynucleotidyl-transferase (TdT) (). 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 entry represents terminal deoxynucleotidyl-transferase (TdT) and the DNA-directed DNA/RNA polymerase mu. The latter is a gap-filling polymerase involved in repair of DNA double-strand breaks by non-homologous end joining [, ]. | Short Name: | TdT/Mu |
| DB identifier | Type | Name |
|---|---|---|
| IPR002054 | Domain | DNA-directed DNA polymerase X |
| IPR010996 | Domain | DNA polymerase beta-like, N-terminal domain |
| IPR018944 | Domain | DNA polymerase lambda, fingers domain |
| IPR001357 | Domain | BRCT domain |
| IPR002934 | Domain | Polymerase, nucleotidyl transferase domain |
| IPR019843 | Binding_site | DNA polymerase family X, binding site |
