<p>Cytidine deaminase (<db_xref db="EC" dbkey="3.5.4.5"/>) (cytidine aminohydrolase) catalyzes the hydrolysis of cytidine into uridine and ammonia while deoxycytidylate deaminase (<db_xref db="EC" dbkey="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 [<cite idref="PUB00000364"/>, <cite idref="PUB00002807"/>]. 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.</p><p>Such a region is also found in other proteins [<cite idref="PUB00005022"/>, <cite idref="PUB00005412"/>]:</p><ul><li>Yeast cytosine deaminase (<db_xref db="EC" dbkey="3.5.4.1"/>) (gene FCY1) which transforms cytosine into uracil.</li><li>Mammalian apolipoprotein B mRNA editing protein, responsible for the postranscriptional editing of a CAA codon into a UAA (stop) codon in the APOB mRNA.</li><li>Riboflavin biosynthesis protein ribG, which converts 2,5-diamino-6-(ribosylamino)-4(3H)-pyrimidinone 5'-phosphate into 5-amino-6-(ribosylamino)-2,4(1H,3H)-pyrimidinedione 5'-phosphate.</li><li> <taxon tax_id="1396">Bacillus cereus</taxon> blasticidin-S deaminase (<db_xref db="EC" dbkey="3.5.4.23"/>), which catalyzes the deamination of the cytosine moiety of the antibiotics blasticidin S, cytomycin and acetylblasticidin S.</li><li> <taxon tax_id="1423">Bacillus subtilis</taxon> protein comEB. This protein is required for the binding and uptake of transforming DNA.</li><li>B. subtilis hypothetical protein yaaJ.</li><li> <taxon tax_id="562">Escherichia coli</taxon> hypothetical protein yfhC.</li><li>Yeast hypothetical protein YJL035c.</li></ul> APOBEC/CMP deaminase, zinc-binding