MutT is a small bacterial protein (~12-15Kd) involved in the GO system [<cite idref="PUB00002202"/>] responsible for removing an oxidatively damaged form of guanine (8-hydroxy- guanine or 7,8-dihydro-8-oxoguanine) from DNA and the nucleotide pool. 8-oxo-dGTP is inserted opposite dA and dC residues of template DNA with near equal efficiency, leading to A-T to G-C transversions. MutT specifically degrades 8-oxo-dGTP to the monophosphate, with the concomitant release of pyrophosphate. A short conserved N-terminal region of mutT (designated the MutT domain) is also found in a variety of other prokaryotic, viral and eukaryotic proteins [<cite idref="PUB00004433"/>, <cite idref="PUB00003856"/>, <cite idref="PUB00002808"/>, <cite idref="PUB00006677"/>]. <p>The generic name `NUDIX hydrolases' (NUcleoside DIphosphate linked to some other moiety X) has been coined for this domain family [<cite idref="PUB00006662"/>]. The family can be divided into a number of subgroups, of which MutT anti- mutagenic activity represents only one type; most of the rest hydrolyse diverse nucleoside diphosphate derivatives (including ADP-ribose, GDP- mannose, TDP-glucose, NADH, UDP-sugars, dNTP and NTP).</p>