Abstract
The alternative streptococcal σ-factor and master competence regulator, σX, stimulates transcription from competence promoters, in vitro. As the only known alternative σ-factor in streptococci, σX expression is tightly controlled in each species and has a specific physiological role. Pneumococcal transformation also requires the DNA binding activity of ComW, a known σX activator and stabilizer. Mutations to the housekeeping σ factor, σA, partially alleviate the ComW requirement, suggesting that ComW is a key player in the σ factor swap during the pneumococcal competence response. However, there is no evidence of a direct ComW – RNA polymerase interaction. Furthermore, if and how ComW functions directly at combox promoters is still unknown. Here we report that a DNA-binding ComW variant, ComΔ6, can stimulate transcription from σX promoters in vitro.
Highlights
Streptococci are Gram-positive commensal cocci for a wide range of animal hosts, including humans
ΣX might have a lower affinity for RNA polymerase (RNAP) than σA, a trait shared among multiple alternative σ-factors (Gruber and Gross, 2003), so excess σX could increase the amount of σX holo-enzyme formation
As we hypothesized that ComW is an active and important member of the competence-specific holo-enzyme, we examined how ComW 6 affected in vitro transcription (IVT) from σX promoters
Summary
Streptococci are Gram-positive commensal cocci for a wide range of animal hosts, including humans. Natural genetic transformation (NGT) was discovered in the pneumococcus (Griffith, 1928; Avery and MacLeod, 1944), and subsequently the genes required for transformation have been found in the genomes of streptococci from all species groups (Håvarstein, 2010). Their genomes encode transcriptional regulators and apparatuses that enable exogenous DNA uptake and genetic recombination. Pneumococci primed for transformation must develop competence, a transient state marked by a shift in both transcriptomic and proteomic profiles, including two waves of new gene transcription, yielding early and late competence gene groups (Peterson et al, 2000; Fontaine et al, 2010; Gao et al, 2014; Khan et al, 2016, 2017). All bacteria produce the principal σ factor σA, responsible for most gene transcription, and many produce multiple alternative σ factors that promote specific cellular responses, σX is the only alternative σ factor produced in pneumococcus (Håvarstein, 2010), and sigX expression is strictly linked to competence development
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