- Escherichia coli orf17 codes for a nucleoside triphosphate pyrophosphohydrolase member of the MutT family of proteins. Cloning, purification, and characterization of the enzyme. O'Handley, S.F., Frick, D.N., Bullions, L.C., Mildvan, A.S., Bessman, M.J. J. Biol. Chem. (1996)