A tellurite-resistance genetic determinant from phytopathogenic pseudomonads encodes a thiopurine methyltransferase: evidence of a widely-conserved family of methyltransferases.

A tellurite-resistance genetic determinant was isolated from the pea blight pathogen Pseudomonas syringae pathovar pisi by a shotgun strategy involving a tellurite-selective screening in Escherichia coli. A 1.65 kb tellurite resistance insert was obtained and analysed. It harbours a single complete and functional ORF encoding a deduced protein of 24, 445 Da. The deduced AA sequence shows significant similarities with the complete human thiopurine methyltransferase enzyme, a methyltransferase from Synechocystis and a methyltransferase-like sequence from Bordetella pertussis. The encoded thiopurine methyltransferase activity was demonstrated using a radiochemical microassay for the methylation of 6-mercaptopurine. This gene was detected in most P. syringae legume pathogens.