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The GtaR protein negatively regulates transcription of the gtaRI operon and modulates gene transfer agent (RcGTA) expression in Rhodobacter capsulatus
Author(s) -
Leung Molly M.,
Brimacombe Cedric A.,
Spiegelman G. B.,
Beatty J. Thomas
Publication year - 2012
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.1365-2958.2011.07963.x
Subject(s) - rhodobacter , biology , operon , mutant , gene , transcription (linguistics) , promoter , mutagenesis , transcription factor , regulation of gene expression , directed mutagenesis , microbiology and biotechnology , gene expression , genetics , linguistics , philosophy
Summary The gtaI gene of Rhodobacter capsulatus encodes an N ‐acyl‐homoserine lactone (acyl‐HSL) synthase. Immediately 5′ of the gtaI gene is ORF rcc00328 that encodes a potential acyl‐HSL receptor protein. A combination of genetic and biochemical approaches showed that rcc00328 (renamed gtaR ) modulates the production of a genetic exchange element called the gene transfer agent (RcGTA), and regulates the transcription of gtaI . Although gtaI mutants exhibited decreased levels of RcGTA production, mutagenesis of gtaR did not, whereas a gtaR/gtaI double mutant produced wild‐type levels of RcGTA. Because mutagenesis of gtaR suppressed the effect of the gtaI mutation, we suggest that the GtaR protein is a negative transcriptional regulator of RcGTA gene expression. We discovered that the gtaR and gtaI genes are co‐transcribed, and also negatively regulated by the GtaR protein in the absence of acyl‐HSL. A His‐tagged GtaR protein was purified, and DNA‐binding experiments revealed a binding site in the promoter region of the gtaRI operon. This GtaR protein did not bind to the RcGTA promoter region, and therefore modulation of RcGTA production appears to require at least one additional factor. We found that RcGTA production was stimulated by spent media from other species, and identified exogenous acyl‐HSLs that induce RcGTA.