Open AccessCatM Regulation of the benABCDE Operon: Functional Divergence of Two LysR-Type Paralogs in Acinetobacter baylyi ADP1
Author(s) -
Obidimma Ezezika,
Lauren S. Collier-Hyams,
Haley A. Dale,
Andrew Burk,
Ellen L. Neidle
Publication year - 2006
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.72.3.1749-1758.2006
Subject(s) - operon , biology , transcription (linguistics) , gene , point mutation , effector , catabolite repression , genetics , repressor , transcriptional regulation , regulation of gene expression , transcription factor , microbiology and biotechnology , biochemistry , mutation , mutant , linguistics , philosophy
Two LysR-type transcriptional regulators, BenM and CatM, control benzoate consumption by the soil bacteriumAcinetobacter baylyi ADP1. These homologs play overlapping roles in the expression of multiple genes. This study focuses on thebenABCDE operon, which initiates benzoate catabolism. At this locus, BenM and CatM each activate transcription in response to the catabolitecis ,cis -muconate. BenM, but not CatM, additionally responds to benzoate as an effector. Regulation by CatM alone is insufficient for growth on benzoate as the sole carbon source. However, three point mutations independently increased CatM-activatedbenA transcription and enabled growth on benzoate without BenM. Two mutations generate variants with one amino acid change in the 303-residue CatM, CatM(V158M) and CatM(R156H). These substitutions affected regulation ofbenA differently than that ofcatB , another CatM-regulated gene involved in benzoate catabolism. In relation to CatM, CatM(V158M) increasedcis ,cis -muconate-dependent transcription ofbenA but decreased that ofcatB . CatM(R156H) increased effector-independent expression ofcatB compared to CatM. In contrast,cis ,cis -muconate was required with CatM(R156H) to activate unusually highbenA expression. Thus, induction bycis ,cis -muconate depends on both the sequence of CatM and the promoter. A point mutation at position −40 of thebenA promoter enhanced CatM-activated gene expression and altered regulation by CatM(R156H). BenM and CatM bound to the same locations onben region DNA. The frequency with which spontaneous mutations allow CatM to substitute for BenM might predict that one regulator would be sufficient for controlling benzoate consumption. This prediction is discussed in light of current and previous studies of the BenM-CatM regulon.