A protein having similarity with methylmalonyl-CoA mutase is required for the assimilation of methanol and ethanol by Methylobacterium extorquens AM1

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Abstract
A 4·0 kb region of Methylobacterium extorquens AM1 DNA which complements three mutants unable to convert acetyl-CoA to glyoxylate (and therefore defective in the assimilation of methanol and ethanol) has been isolated 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, which was designated meaA ; it encodes a protein having similarity with methylmalonyl- CoA mutase. However, methylmalonyl-CoA mutase was measured in extracts of one of the mutants and the specific activity was found to be similar to that in extracts of wild-type cells. Furthermore, although the predicted meaA gene product has the proposed cobalamin-binding site, it does not contain a highly conserved sequence (RIARNT) which is present in all known methylmalonyl- CoA mutases; meaA may therefore encode a novel vitamin-B12-dependent enzyme. The predicted polypeptide encoded by the second ORF did not have similarity with any known 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.