{PDOC00452}
{PS00522; DNA_POLYMERASE_X}
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* DNA polymerase family X signature *
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DNA polymerases (EC  2.7.7.7) can  be  classified,  on  the  basis of sequence
similarity [1],  into  at  least  four  different  groups:  A, B, C and X. DNA
polymerases that belong to family X are listed below [2]:

 - Vertebrate polymerase beta, involved in DNA repair.
 - Yeast polymerase IV (POL4) [3], an  enzyme with similar characteristics  to
   that of the mammalian polymerase beta.
 - Terminal deoxynucleotidyltransferase   (TdT)  (EC 2.7.7.31).  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.
 - African Swine Fever virus protein O174L [4].
 - Fission yeast hypothetical protein SpAC2F7.06c.

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
[5] to be involved in primer binding in polymerase beta.

-Consensus pattern: G-[SG]-[LFY]-x-R-[GE]-x(3)-[SGCL]-x-D-[LIVM]-D-
                    [LIVMFY](3)-x(2)-[SAP]
                    [The 2 D's and the R are involved in ssDNA binding]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: May 2004 / Text revised.

[ 1] Ito J., Braithwaite D.K.
     "Compilation and alignment of DNA polymerase sequences."
     Nucleic Acids Res. 19:4045-4057(1991).
     PubMed=1870963
[ 2] Matsukage A., Nishikawa K., Ooi T., Seto Y., Yamaguchi M.
     "Homology between mammalian DNA polymerase beta and terminal
     deoxynucleotidyltransferase."
     J. Biol. Chem. 262:8960-8962(1987).
     PubMed=3597402
[ 3] Prasad R., Widen S.G., Singhal R.K., Watkins J., Prakash L., Wilson S.H.
     "Yeast open reading frame YCR14C encodes a DNA beta-polymerase-like
     enzyme."
     Nucleic Acids Res. 21:5301-5307(1993).
     PubMed=8265341
[ 4] Yanez R.J., Rodriguez J.M., Nogal M.L., Yuste L., Enriquez C.,
     Rodriguez J.F., Vinuela E.
     "Analysis of the complete nucleotide sequence of African swine fever
     virus."
     Virology 208:249-278(1995).
     PubMed=11831707
[ 5] Date T., Yamamoto S., Tanihara K., Nishimoto Y., Matsukage A.
     "Aspartic acid residues at positions 190 and 192 of rat DNA polymerase
     beta are involved in primer binding."
     Biochemistry 30:5286-5292(1991).
     PubMed=2036395

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