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* Thymidine kinase cellular-type signature *
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Thymidine kinase (TK) (EC 2.7.1.21) is an ubiquitous enzyme that catalyzes the
ATP-dependent phosphorylation of thymidine.   A comparison of TK sequences has
shown [1,2,3] that there are two different families of TK.   One family groups
together TK from herpesviruses as well as cellular thymidylate kinases,  while
the second family currently consists of TK from the following sources:

 - Vertebrates.
 - Escherichia coli.
 - Bacteriophage T4.
 - Poxviruses.
 - African swine fever virus (ASF).
 - Fish lymphocystis disease virus (FLDV).

As a signature pattern  for  this family of TK we selected a  conserved region
which is located in the C-terminal section of these enzymes.

-Consensus pattern: [GA]-x-[DE]-x-Y-x-[STAP]-x-C-[NR]-x-[CH]-[LIVMFYWH]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for TK from FLDV which is highly  divergent  compared to the other members of
 this family.
-Other sequence(s) detected in SWISS-PROT: NONE.

-Note: the proteins belonging to this family also contains a copy  of the ATP-
 binding motif 'A' (P-loop) in their N-terminal extremity.

-Last update: October 1993 / Pattern and text revised.

[ 1] Boyle D.B., Coupar B.E.H., Gibbs A.J., Seigman L.J., Both G.W.
     Virology 156:355-365(1987).
[ 2] Blasco R., Lopez-Otin C., Munoz M., Bockamp E.-O., Simon-Mateo C.,
     Vinuela E.
     Virology 178:301-304(1990).
[ 3] Robertson G.R., Whalley J.M.
     Nucleic Acids Res. 16:11303-11317(1988).