DNA polymerases (EC 22.214.171.124) can be classified, on the basis of sequence
similarity , into at least four different groups: A, B, C and X. DNA
polymerases that belong to family X are listed below :
Vertebrate polymerase β, involved in DNA repair.
Yeast polymerase IV (POL4) , an enzyme with similar characteristics to
that of the mammalian polymerase β.
Terminal deoxynucleotidyltransferase (TdT) (EC 126.96.36.199). TdT catalyzes
the elongation of polydeoxynucleotide chains by terminal addition. One of
the functions of this enzyme is the addition of nucleotides at the junction
of rearranged Ig heavy chain and T cell receptor gene segments during the
maturation of B and T cells.
These enzymes are small (about 40 Kd) compared with other polymerases and
their reaction mechanism operates via a distributive mode, i.e. they
dissociate from the template-primer after addition of each nucleotide.
As a signature pattern for this family of DNA polymerases, we selected a
highly conserved region that contains a conserved arginine and two conserved
aspartic acid residues. The latter together with the arginine have been shown
 to be involved in primer binding in polymerase β.
May 2004 / Text revised.
PROSITE method (with tools and information) covered by this documentation:
Ito J. Braithwaite D.K.
Compilation and alignment of DNA polymerase sequences.
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