Abstract
BackgroundThe expression of genes in Corynebacterium glutamicum, a Gram-positive non-pathogenic bacterium used mainly for the industrial production of amino acids, is regulated by seven different sigma factors of RNA polymerase, including the stress-responsive ECF-sigma factor SigH. The sigH gene is located in a gene cluster together with the rshA gene, putatively encoding an anti-sigma factor. The aim of this study was to analyze the transcriptional regulation of the sigH and rshA gene cluster and the effects of RshA on the SigH regulon, in order to refine the model describing the role of SigH and RshA during stress response.ResultsTranscription analyses revealed that the sigH gene and rshA gene are cotranscribed from four sigH housekeeping promoters in C. glutamicum. In addition, a SigH-controlled rshA promoter was found to only drive the transcription of the rshA gene. To test the role of the putative anti-sigma factor gene rshA under normal growth conditions, a C. glutamicum rshA deletion strain was constructed and used for genome-wide transcription profiling with DNA microarrays. In total, 83 genes organized in 61 putative transcriptional units, including those previously detected using sigH mutant strains, exhibited increased transcript levels in the rshA deletion mutant compared to its parental strain. The genes encoding proteins related to disulphide stress response, heat stress proteins, components of the SOS-response to DNA damage and proteasome components were the most markedly upregulated gene groups. Altogether six SigH-dependent promoters upstream of the identified genes were determined by primer extension and a refined consensus promoter consisting of 45 original promoter sequences was constructed.ConclusionsThe rshA gene codes for an anti-sigma factor controlling the function of the stress-responsive sigma factor SigH in C. glutamicum. Transcription of rshA from a SigH-dependent promoter may serve to quickly shutdown the SigH-dependent stress response after the cells have overcome the stress condition. Here we propose a model of the regulation of oxidative and heat stress response including redox homeostasis by SigH, RshA and the thioredoxin system.
Highlights
The expression of genes in Corynebacterium glutamicum, a Gram-positive non-pathogenic bacterium used mainly for the industrial production of amino acids, is regulated by seven different sigma factors of RNA polymerase, including the stress-responsive ECF-sigma factor SigH
Due to its small size of 267 nucleotides (89 amino acids), the rshA gene has not been annotated in two other C. glutamicum genome sequences, but it can be found there by using a BLASTX search
It is interesting to note that the absence of the rshA gene in the annotation of one of the C. glutamicum genome sequences [4] apparently misled the authors of a recent study [13], who picked the wrong ortholog from C. glutamicum in order to check for a functional complementation of rsrA in Streptomyces
Summary
The expression of genes in Corynebacterium glutamicum, a Gram-positive non-pathogenic bacterium used mainly for the industrial production of amino acids, is regulated by seven different sigma factors of RNA polymerase, including the stress-responsive ECF-sigma factor SigH. C. glutamicum has been studied extensively because of its biotechnological application in the production of various amino acids It is of increasing importance as a model organism for other corynebacteria with biotechnological or medical significance, as well as for the species of related genera [1,2,3]. The functions of the genes encoding transcriptional regulators or sigma factors of RNA polymerase may be assigned using comparative genomics, their role and connections in cell regulatory networks could hardly be deduced on the basis of genome sequences alone. Comparative transcriptome analyses of wild-type and mutant strains provide extensive sets of data enabling the connections between the nodes of the regulatory network to be determined
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