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* Cytidine and deoxycytidylate deaminases zinc-binding region signature *
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Cytidine deaminase   (EC  3.5.4.5)  (cytidine  aminohydrolase)  catalyzes  the
hydrolysis of   cytidine   into  uridine  and  ammonia  while  deoxycytidylate
deaminase  (EC 3.5.4.12)  (dCMP  deaminase)  hydrolyzes  dCMP  into dUMP. Both
enzymes are known  to bind zinc and to require it for their catalytic activity
[1,2]. These  two  enzymes  do  not  share  any  sequence  similarity with the
exception of a region that  contains  three conserved histidine  and  cysteine
residues which are thought to be involved in the binding of the catalytic zinc
ion.

Such a region is  also found in two other proteins that are highly similar [3]
to deoxycytidylate deaminase; these proteins are:

 - A 21 Kd protein in the comE  operon from Bacillus subtilis.  This operon is
   required for the binding and uptake of transforming DNA.
 - Caenorhabditis elegans hypothetical protein ZK643.2.

We have derived a signature pattern for this zinc-binding region.

-Consensus pattern: [CH]-A-E-x-[STN]-A-[LIVM]-x(18,26)-P-C-x(2)-C-x(3)-[LIVM]-
                    x-[EQ]
                    [The C's and H are zinc ligands]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in SWISS-PROT: NONE.
-Last update: June 1994 / Pattern and text revised.

[ 1] Yang C., Carlow D., Wolfenden R., Short S.A.
     Biochemistry 31:4168-4174(1992).
[ 2] Moore J.T., Silversmith R.E., Maley G.F., Maley F.
     J. Biol. Chem. 268:2288-2291(1993).
[ 3] Bairoch A.
     Unpublished observations (1993).