The Saccharomyces cerevisiae YOR163w gene encodes a diadenosine 5 ',5 '''-P-1,P-6-hexaphosphate (Ap(6)A) hydrolase member of the MutT motif (nudix hydrolase) family

The YOR163w open reading frame on chromosome XV of the Saccharomyces cerevi siae genome encodes a member of the MutT motif (nudix hydrolase) family of enzymes of M-r 21,443. By cloning and expressing this gene in Escherichia c oli and S. cerevisiae, we have shown the product to be a (di)adenosine poly phosphate hydrolase with a previously undescribed substrate specificity. Di adenosine 5',5'''-P-1,P-6-hexaphosphate is the preferred substrate, and hyd rolysis in (H2O)-O-18 shows that ADP and adenosine 5'-tetraphosphate are pr oduced by attack at P beta and AMP and adenosine 5'-pentaphosphate are prod uced by attack at P-alpha with a K-m of 56 mu m and k(cat) of 0.4 s(-1). Di adenosine 5',5'''-P-1,P-5-pentaphosphate, adenosine 5'-pentaphosphate, and adenosine 5'-tetraphosphate are also substrates, but not diadenosine 5',5"- P-1,P-4-tetraphosphate or other dinucleotides, mononucleotides, nucleotide sugars, or nucleotide alcohols. The enzyme, which was shown to be expressed in log phase yeast cells by immunoblotting, displays optimal activity at p H 6.9, 50 degrees C, and 4-10 mM Mg2+ (or 200 mu M Mn2+). It has an absolut e requirement for a reducing agent, such as dithiothreitol (1 mM), and is i nhibited by Ca2+ with an IC50 of 3.3 mM and F- (noncompetitively) with a K- i of 80 mu M. Its function may be to eliminate potentially toxic dinucleosi de polyphosphates during sporulation.