codes for a C5– cytosine MTase from H. pylori. It was observed that expression of M.HpyAVIB in E. coli enhanced the mutation rate. hpyAVIBM itself was mutated to give rise to different variants. Purified MTase variants showed relaxed substrate specificity. Thus, hpyAVIBM presents an interesting example of allelic variations in H. pylori where changes in the nucleotide sequence result in proteins with new properties.