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Complex interplay between the LysR‐type regulator AtzR and its binding site mediates atzDEF activation in response to two distinct signals
Author(s) -
Porrúa Odil,
Platero Ana Isabel,
Santero Eduardo,
Del Solar Gloria,
Govantes Fernando
Publication year - 2010
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2010.07100.x
Subject(s) - repressor , cyanuric acid , biology , operon , footprinting , binding site , inducer , activator (genetics) , biochemistry , dna footprinting , protein subunit , transcription (linguistics) , allosteric regulation , regulator , stereochemistry , transcription factor , microbiology and biotechnology , dna binding protein , chemistry , mutant , gene , enzyme , linguistics , philosophy , organic chemistry , melamine
Summary AtzR is a LysR‐type regulator responsible for activation of the cyanuric acid utilization operon atzDEF . AtzR binds the P atzDEF promoter region at a strong recognition element, designated the repressor binding site, and a weaker binding determinant, the activator binding site (ABS). AtzR activates transcription in response to two dissimilar signals, nitrogen limitation and cyanuric acid. In the present work we analyse the structure and function of the cis‐ acting elements involved in AtzR activation of atzDEF . Hydroxyl radical footprinting assays revealed that the ABS is composed of three functional subsites spaced at one helix‐turn intervals. Two modes of interaction with the ABS are detected in vitro : AtzR binds at the ABS‐2 and ABS‐3 subsites in the absence of inducer, and relocates to interact with the ABS‐1 and ABS‐2 subsites in the presence of cyanuric acid. In vivo mutational analysis indicates that ABS‐1 and ABS‐2 are required for full P atzDEF activation in all conditions. In contrast, ABS‐3 acts as a ‘subunit trap’ that hinders productive AtzR interactions with ABS‐1 and ABS‐2. Our results strongly suggest an activation model in which cyanuric acid and nitrogen limitation cooperate to reposition AtzR from an inactive, ABS‐3 bound configuration to an active, ABS‐1‐ and ABS‐2‐bound configuration.