σECF factors of gram-positive bacteria

Bacteria are frequently exposed to a range of different circumstances in which the activation of adaptive mechanisms is essential for cell maintenance and survival. The modulation of such activity is intricately driven through gene regulation, involving diverse events at the transcriptional, translational, and posttranslational levels. Thus, transcription initiation could be considered the major step in the control of bacterial genes. In its inactive state, RNAP consists of only its core, which is formed by the subunits α 2 , β, β’, and ω, whereas in association with a sigma factor, the core transiently becomes an RNAP holoenzyme, whose function is to transcribe DNA into RNA. In association with the core RNAP, the sigma factors provide a dynamic mechanism for cellular responses performed through redirecting transcription initiation. Not only do these factors include many, if not all, of the determinants of promoter recognition, they also contribute to DNA strand separation during the initiation of transcription. Because these proteins preferentially recognize specific promoters in the genome, the generation of distinct combinations of several of these proteins with RNAP provides an effective means of modulating transcription profiles, altering the expression of large groups of genes, or regulons, in response to various environmental stimuli, and changing extracellular and/ or intracellular conditions in accord with the physiological requirements of the organism. In some cases, the genes that constitute a specific regulon have a clearly defined primary function, such as those regulated by the sporulation sigma factors of B. subtilis, while in other cases, these genes contribute to multiple processes, such as those related to the stationary phase of growth and general stress response regulated by the alternative sigma factor σ in Listeria monocytogenes. In the case of bacterial pathogens in particular, the mechanism of changing sigma factors regulates the expression of virulence genes, encoding proteins whose functions are essential for the bacterium to effectively establish an infection, and *Correspondence to: Vasco Azevedo; Email: [email protected] Submitted: 10/07/2013; Revised: 06/05/2014; Accepted: 06/06/2014; Published Online: 06/12/2014 http://dx.doi.org/10.4161/viru.29514 σECF factors of gram-positive bacteria A focus on Bacillus subtilis and the CMNR group