A Riboswitch Regulates Expression of the Coenzyme B ₁₂ -Independent Methionine Synthase in <i>Mycobacterium tuberculosis</i> : Implications for Differential Methionine Synthase Function in Strains H37Rv and CDC1551

Abstract

We observed vitamin B(12)-mediated growth inhibition of Mycobacterium tuberculosis strain CDC1551. The B(12) sensitivity was mapped to a polymorphism in metH, encoding a coenzyme B(12)-dependent methionine synthase. Vitamin B(12)-resistant suppressor mutants of CDC1551 containing mutations in a B(12) riboswitch upstream of the metE gene, which encodes a B(12)-independent methionine synthase, were isolated. Expression analysis confirmed that the B(12) riboswitch is a transcriptional regulator of metE in M. tuberculosis.