A PROTEIN HAVING SIMILARITY WITH METHYLMALONYL-COA MUTASE IS REQUIREDFOR THE ASSIMILATION OF METHANOL AND ETHANOL BY METHYLOBACTERIUM-EXTORQUENS AM1

A 4.0 kb region of Methylobacterium extorquens AM1 DNA which complemen ts three mutants unable to convert acetyl-CoA to glyoxylate (and there fore defective in the assimilation of methanol and ethanol) has been i solated and sequenced. It contains two ORFs and the 3'-end of a third one. The mutations in all three mutants mapped within the first ORF, w hich was designated meaA; it encodes a protein having similarity with methylmalonyl-CoA mutase. However, methylmalonyl-CoA mutase was measur ed in extracts of one of the mutants and the specific activity was fou nd to be similar to that in extracts of wild-type cells. Furthermore, although the predicted meaA gene product has the proposed cobalamin-bi nding site, it does not contain a highly conserved sequence (RIARNT) w hich is present in all known methylmalonyl-CoA mutases; meaA may there fore encode a novel vitamin-B-12-dependent enzyme. The predicted polyp eptide encoded by the second ORF did not have similarity with any know n proteins. The partial ORF encoded a protein with similarity with the 3-oxoacyl-[acyl-carrier-protein] reductases; it was not essential for growth on methanol or ethanol.