A riboswitch regulates expression of the coenzyme B12- independent methionine synthase in Mycobacterium tuberculosis: Implications for differential methionine synthase function in strains H37Rv and CDC1551

We observed vitamin B12-mediated growth inhibition of Mycobacterium tuberculosis strain CDC1551. The B12 sensitivity was mapped to a polymorphism in metH, encoding a coenzyme B12-dependent methionine synthase. Vitamin B12-resistant suppressor mutants of CDC1551 containing mutations in a B12 riboswitch upstream of the metE gene, which encodes a B12-independent methionine synthase, were isolated. Expression analysis confirmed that the B12 riboswitch is a transcriptional regulator of metE in M. tuberculosis. Copyright © 2007, American Society for Microbiology. All Rights Reserved.