Mutational analysis of the Escherichia coli melR gene suggests a two-state concerted model to explain transcriptional activation and repression in the melibiose operon.

Journal of Bacteriology
Christina KahramanoglouStephen J W Busby

Abstract

Transcription of the Escherichia coli melAB operon is regulated by the MelR protein, an AraC family member whose activity is modulated by the binding of melibiose. In the absence of melibiose, MelR is unable to activate the melAB promoter but autoregulates its own expression by repressing the melR promoter. Melibiose triggers MelR-dependent activation of the melAB promoter and relieves MelR-dependent repression of the melR promoter. Twenty-nine single amino acid substitutions in MelR that result in partial melibiose-independent activation of the melAB promoter have been identified. Combinations of different substitutions result in almost complete melibiose-independent activation of the melAB promoter. MelR carrying each of the single substitutions is less able to repress the melR promoter, while MelR carrying some combinations of substitutions is completely unable to repress the melR promoter. These results argue that different conformational states of MelR are responsible for activation of the melAB promoter and repression of the melR promoter. Supporting evidence for this is provided by the isolation of substitutions in MelR that block melibiose-dependent activation of the melAB promoter while not changing melibiose-independe...Continue Reading

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Citations

Mar 19, 2008·Nucleic Acids Research·Shivanthi SamarasingheStephen J W Busby
Feb 26, 2008·Journal of Bacteriology·Patricia Domínguez-CuevasSilvia Marqués
Jan 8, 2013·Journal of Bacteriology·Axel Cournac, Jacqueline Plumbridge
Feb 13, 2015·Proceedings of the National Academy of Sciences of the United States of America·Parameswaran HariharanLan Guan
Oct 10, 2014·The Journal of Biological Chemistry·Parameswaran Hariharan, Lan Guan
Apr 11, 2021·FEMS Microbiology Reviews·Daniel Cortés-AvalosJ Antonio Ibarra

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