Abstract
Extracytoplasmic function (ECF) σ factors have roles related to cell envelope and/or cell membrane functions, in addition to other cellular functions. Without cell-surface stresses, ECF σ factors are sequestered by the cognate anti-σ factor, leading to inactivation and the resultant repression of regulons due to the inhibition of transcription of their own genes. Bacillus subtilis has seven ECF σ factors including σX and σM that transcribe their own structural genes. Here, we report that glucose addition to the medium induced sigX and sigM transcription independent of their anti-σ factors. This induction was dependent on an intracellular acetyl-CoA pool. Transposon mutagenesis searching for the mutants showing no induction of sigX and sigM revealed that the cshA gene encoding DEAD-box RNA helicase is required for gene induction. Global analysis of the acetylome in B. subtilis showed CshA has two acetylated lysine residues. We found that in a cshA mutant with acetylation-abolishing K to R exchange mutations, glucose induction of sigX and sigM was abolished and that glucose addition stimulated acetylation of CshA in the wild type strain. Thus, we present a model wherein glucose addition results in a larger acetyl-CoA pool, probably leading to increased levels of acetylated CshA. CshA is known to associate with RNA polymerase (RNAP), and thus RNAP with acetylated CshA could stimulate the autoregulation of sigX and sigM. This is a unique model showing a functional link between nutritional signals and the basal transcription machinery.
Highlights
The association of σ factor with RNA polymerase (RNAP) determines the specific binding of the RNAP holoenzyme to target promoters (Helmann and Chamberlin, 1988)
To clarify which σ factors other than σA are responsible for glucose induction (GI), we introduced several mutations in the genes encoding σ factors and examined expression of the promoter for yjbC fused to lacZ
In the strain with CshA bearing two Extracytoplasmic function σ factor genes have been shown to be induced mainly by cell envelope and cell membrane stresses through a mechanism involving anti-σ factor embedded in the cell membrane
Summary
The association of σ factor with RNAP determines the specific binding of the RNAP holoenzyme to target promoters (Helmann and Chamberlin, 1988). In Bacillus subtilis, seven ECF σ factors, σM, σV, σW, σX, σY, σZ, and σYlaC are encoded in the genome (Helmann, 2016). In many cases, these σ factors recognize similar nucleotide sequences. ΣM, σV, σW, and σX bind to the consensus −35 and −10 elements, (T)GAAACNT and CGT(C/A)T, respectively (Helmann, 2016) As a result, these σ-factor regulons overlap, yet there are genes transcribed by a single ECF σ factor. The σM regulon includes >60 genes such as core genes for cell wall biogenesis and cell division (rodA, divIC, mreBCDminCD, and murBdivIB), regulatory genes (spx and abh), and the bacitracin resistance gene bcrC (Cao and Helmann, 2002; Thackray and Moir, 2003; Eiamphungporn and Helmann, 2008; Luo and Helmann, 2009)
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