About this Research Topic
The transcription of bacterial genes driven by DNA-dependent RNA polymerase (RNAP) is the first step in gene expression. The RNAP core is a large, complex enzyme consisting of the subunits α2ββ´ω. The additional sigma (σ) subunit (factor), which binds to the RNAP core to form the RNAP holoenzyme, is responsible for promoter recognition and subsequent transcription initiation. Thus, σ factors are the regulators that are necessary for the transcription initiation of each bacterial gene. Bacteria usually contain several different factors. Most σ factors belong to the σ70-family, while some bacteria also contain a σ factor of the σ54-family. Only a single factor was found in Mycoplasma genitalium, whereas 7 factors were reported in Escherichia coli, 13 in Mycobacterium tuberculosis, 17 in Bacillus subtilis, 34 in Rhodococcus jostii and over 60 in Streptomyces species.
There are four groups of sigma factors of the σ70-family differing by number of domains and functions. Group 1 contains mostly one primary σ factor, which controls expression of most genes under non-stressed conditions. Group 2 is represented by primary-like σ factor mostly involved in general stress response and/or expression in the stationary growth phase. Group 3 σ factors control specific functions such as flagella formation, and group 4 (called also extracytoplasmic function, ECF) are mostly involved in various stress responses. The individual types of RNAP holoenzyme recognize distinct classes of promoters having different key recognition DNA sequences. Sigma factors thus function as global regulators of transcription, which switch expression of large gene groups (regulons) in response to various environmental stimuli or changing extracellular or intracellular conditions. Since the activities of the different holo-RNAPs and the respective promoters orchestrate the cell metabolism in complex responses to various nutrition, growth, and stress conditions, engineering σ factors has recently become a promising field in biotechnology and synthetic biology, particularly for the development of synthetic transcriptional control.
The studies included into this Research Topic may cover a broad range of topics concerning σ factors, their regulons, and regulatory networks:
• Mechanisms of stress responses regulated by specific sigma factors
• Mechanisms of control of sigma factors by anti-sigma factors mediated by signal transduction
• Genome wide analysis of specific sigma regulons
• Role of sigma factors in pathogenesis
• Role of sigma factors in development
• Description of promoter classes recognized by specific sigma factors
• Engineering of sigma factors and promoters for biotechnological purposes
• Sigma regulatory networks
• Role of sigma factors in biofilm formation
• Structural relationship between the binding regions of sigma factors and promoters
This Research Topic welcomes Original Research, Review, and Mini-Review manuscripts focused on a wide range of topics concerning sigma factors and their functions.
Keywords: sigma factor, RNA polymerase, regulon, stress response, transcription initiation, promoter
Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.