EthR, a repressor of the TetR/CamR family implicated in ethionamide resistance in mycobacteria, octamerizes cooperatively on its operator

Jean Engohang-Ndong, David Baillat, Marc Aumercier, Flore Bellefontaine, Gurdyal S. Besra, Camille Locht, Alain R. Baulard

Research output: Contribution to journalShort surveypeer-review

139 Scopus citations


Ethionamide (ETH) is an important second-line anti-tubercular drug used for the treatment of patients infected with multidrug-resistant Mycobacterium tuberculosis. Although ETH is a structural analogue of isoniazid, only little cross-resistance to these two drugs is observed among clinical isolates. Both isoniazid and ETH are pro-drugs that need to be activated by mycobacterlal enzymes to exert their antimicrobial activity. We have recently identified two M. tuberculosis genes, Rv3854c (ethA) and Rv3855 (ethR), involved in resistance to ETH. ethA encodes a protein that belongs to the Flavin-containing monooxygenase family catalysing the activation of ETH. We show here that ethR, which encodes a repressor belonging to the TetR/CamR family of transcriptional regulators, negatively regulates the expression of ethA. By the insertion of the ethA promoter region upstream of the lacZ reporter gene, overexpression of ethR in trans was found to cause a strong inhibition of ethA expression, independently of the presence of ETH in the culture media. Electrophoretic mobility shift assays indicated that EthR interacts directly with the ethA promoter region. This interaction was confirmed by DNA footprinting analysis, which, in addition, identified the EthR-binding region. Unlike other TetR/CamR members, which typically bind 15 bp operators, EthR recognises an unusually long 55 bp region suggesting multimerization of the repressor on its operator. Identification by primer-extension of the ethA transcriptional start site indicated that it is located within the EthR-binding region. Taken together, bacterial two-hybrid experiments and gel filtration assays suggested a dimerization of EthR in the absence of its operator. In contrast, surface plasmon resonance analyses showed that eight EthR molecules bind cooperatively to the 55 bp operator, which represents a novel repression mechanism for a TetR/CamR member.

Original languageEnglish (US)
Pages (from-to)175-188
Number of pages14
JournalMolecular Microbiology
Issue number1
StatePublished - Jan 2004
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


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