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Publication Abstract from PubMed

The Escherichia coli chromosomal relBE operon encodes a toxin-antitoxin system, which is autoregulated by its protein products, RelB and RelE. RelB acts as a transcriptional repressor and RelE functions as a cofactor to enhance the repressor activity of RelB. Here, we present the NMR-derived structure of a RelB dimer and show that a RelB dimer recognizes a hexad repeat in the palindromic operator region through a ribbon-helix-helix motif. Our biochemical data show that two weakly associated RelB dimers bind to the adjacent repeats in the 3'-site of the operator (O(R)) at a moderate affinity (K(d), approximately 10(-5) M). However, in the presence of RelE, a RelB tetramer binds two distinct binding sites within the operator region, each with an enhanced affinity (K(d), approximately 10(-6) M for the low-affinity site, O(L), and 10(-8) M for the high-affinity site, O(R)). We propose that the enhanced affinity for the operator element is mediated by a cooperative DNA binding by a pair of RelB dimers and that the interaction between RelB dimers is strongly augmented by the presence of the cognate toxin RelE.

Structural mechanism of transcriptional autorepression of the Escherichia coli RelB/RelE antitoxin/toxin module.,Li GY, Zhang Y, Inouye M, Ikura M J Mol Biol. 2008 Jun 27;380(1):107-19. Epub 2008 Apr 22. PMID:18501926^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.