The Crc global regulator inhibits the Pseudomonas putida pWW0 toluene/xylene assimilation pathway by repressing the translation of regulatory and structural genes.
In Pseudomonas putida, the expression of the pWW0 plasmid genes for the toluene/xylene assimilation pathway (the TOL pathway) is subject to complex regulation in response to environmental and physiological signals. This includes strong inhibition via catabolite repression, elicited by the carbon sources that the cells prefer to hydrocarbons. The Crc protein, a global regulator that controls carbon flow in pseudomonads, has an important role in this inhibition. Crc is a translational repressor that regulates the TOL genes, but how it does this has remained unknown. This study reports that Crc binds to sites located at the translation initiation regions of the mRNAs coding for XylR and XylS, two specific transcription activators of the TOL genes. Unexpectedly, eight additional Crc binding sites were found overlapping the translation initiation sites of genes coding for several enzymes of the pathway, all encoded within two polycistronic mRNAs. Evidence is provided supporting the idea that these sites are functional. This implies that Crc can differentially modulate the expression of particular genes within polycistronic mRNAs. It is proposed that Crc controls TOL genes in two ways. First, Crc inhibits the translation of the XylR and XylS regulators, thereby reducing the transcription of all TOL pathway genes. Second, Crc inhibits the translation of specific structural genes of the pathway, acting mainly on proteins involved in the first steps of toluene assimilation. This ensures a rapid inhibitory response that reduces the expression of the toluene/xylene degradation proteins when preferred carbon sources become available.
Moreno
Renata
R
Department of Microbial Biotechnology, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, Campus Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
Fonseca
Pilar
P
Rojo
Fernando
F
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001483:Base Sequence; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000235:genetics; D011401:Promoter Regions, Genetic; D016958:Pseudomonas putida / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D014050:Toluene / Q000737:chemistry*; D014158:Transcription, Genetic; D014992:Xylenes / Q000737:chemistry*
D001426:Bacterial Proteins; D009841:Oligonucleotides; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; D014992:Xylenes; C101896:crc protein, Pseudomonas; D014050:Toluene