ANALYSIS OF A RHIZOBIUM-LEGUMINOSARUM GENE ENCODING A PROTEIN HOMOLOGOUS TO GLUTATHIONE S-TRANSFERASES

A novel Rhizobium leguminosarum gene, gstA, the sequence of which indi cated that it was a member of the gene family of glutathione S-transfe rases (GSTs), was identified. The homology was greatest to the GST enz ymes of higher plants. The Rhizobium gstA gene was normally expressed at a very low level. The product of gstA was over-expressed and purifi ed from Escherichia coli. It was shown to bind to the affinity matrix glutathione-Sepharose, but no enzymic GST activity with 1-chloro-2,4-d initrobenzene as substrate was detected, gstA encoded a polypeptide of 203 amino acid residues with a calculated molecular mass of 21990 Da. Transcribed divergently from gstA is another gene, gstR, which was si milar in sequence to the LysR family of bacterial transcriptional regu lators. A mutation in gstR had no effect on the transcription of itsel f or gstA under the growth conditions used here. Mutations in gstA and gstR caused no obvious phenotypic defect and the biological functions of these genes remain to be determined.