NTPase/HAM1. This family consists of the HAM1 protein and pyrophosphate-releasing xanthosine/ inosine triphosphatase. HAM1 protects the cell against mutagenesis by the base analog 6-N-hydroxylaminopurine (HAP) in E. Coli and S. cerevisiae. A Ham1-related protein from Methanococcus jannaschii is a novel NTPase that has been shown to hydrolyze nonstandard nucleotides such as XTP to XMP and ITP to IMP, but not the standard nucleotides, in the presence of Mg or Mn ions. The enzyme exists as a homodimer. The HAM1 protein may be acting as an NTPase by hydrolyzing the HAP triphosphate.
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