Studies on the ADP-ribose pyrophosphatase subfamily of the Nudix hydrolases and tentative identification of trgB, a gene associated with tellurite resistance

Four Nudix hydrolase genes, ysa1 from Saccharomyces cerevisiae, orf209 from Escherichia coli, yqkg from Bacillus subtilis, and hi0398 from Hemophilus influenzae were amplified, cloned into an expression vector, and transforme d into E. coli. The expressed proteins were purified and shown to belong to a subfamily of Nudix hydrolases active on ADP-ribose. Comparison with othe r members of the subfamily revealed a conserved proline 16 amino acid resid ues downstream of the Nudix box, common to all of the ADP-ribose pyrophosph atase subfamily. In this same region, a conserved tyrosine designates anoth er subfamily, the diadenosine polyphosphate pyrophosphatases, while an arra y of eight conserved amino acids is indicative of the NADH pyrophosphatases . On the basis of these classifications, the trgB gene, a tellurite resista nce factor from Rhodobacter sphaeroides, was predicted to designate an ADP- ribose pyrophosphatase. In support of this hypothesis, a highly specific AD P-ribose pyrophosphatase gene from the archaebacterium, Methanococcus janna schii, introduced into E, coli, increased the transformant's tolerance to p otassium tellurite.