The RNA polymerase sigma factor SigA4 (sigA4) is a protein that plays a crucial role in transcription initiation by bacterial RNA polymerase. Sigma factors are essential for promoter recognition and the initiation of transcription by the bacterial core RNA polymerase [1]. They are released from or activated by anti-sigma factors and direct RNA polymerase to express genes required for the cell to adapt to new environments [2]. The sigma factor confers transcriptional specificity to the core RNA polymerase in vitro, indicating its role in directing the initiation of transcription from defined promoter sequences [1]. Furthermore, sigma factors are DNA-binding proteins that contact promoter DNA, and they contain DNA-binding domains that determine promoter specificity [1]. In addition, sigma factors must be bound to core RNA polymerase to direct its use of specific promoters [3].
The sigma factor SigA4 is part of a family of proteins with homology to the major vegetative sigma factor of Escherichia coli, and it directs the RNA polymerase holoenzyme to specific classes of promoter sequences with different consensus in the -35 and -10 regions [1]. Moreover, sigma factors are known to be involved in the regulation of various cellular processes, such as the response to oxidative stress [2], carbohydrate metabolism [4], and the stress response [5]. They also play a role in controlling the transcription of genes according to the growth phase of the cell [6].
References:
[1] M. Merrick, "In a class of its own — the rna polymerase sigma factor σ;54 (σn)", Molecular Microbiology, vol. 10, no. 5, p. 903-909, 1993. https://doi.org/10.1111/j.1365-2958.1993.tb00961.x
[2] B. Butcher, Z. Bao, J. Wilson, P. Stodghill, B. Swingle, M. Filiatraultet al., "The ecf sigma factor, pspto_1043, in pseudomonas syringae pv. tomato dc3000 is induced by oxidative stress and regulates genes involved in oxidative stress response", Plos One, vol. 12, no. 7, p. e0180340, 2017. https://doi.org/10.1371/journal.pone.0180340
[3] M. Shuler, K. Tatti, K. Wade, & C. Moran, "A single amino acid substitution in sigma e affects its ability to bind core rna polymerase", Journal of Bacteriology, vol. 177, no. 13, p. 3687-3694, 1995. https://doi.org/10.1128/jb.177.13.3687-3694.1995
[4] M. Stevens, D. Molenaar, A. Jong, W. Vos, & M. Kleerebezem, "Σ 54-mediated control of the mannose phosphotransferase sytem in lactobacillus plantarum impacts on carbohydrate metabolism", Microbiology, vol. 156, no. 3, p. 695-707, 2010. https://doi.org/10.1099/mic.0.034165-0
[5] B. Sevcikova, "Activity of the streptomyces coelicolor stress-response sigma factor σh is regulated by an anti-sigma factor", Fems Microbiology Letters, vol. 209, no. 2, p. 229-235, 2002. https://doi.org/10.1016/s0378-1097(02)00513-x
[6] M. Fujita, K. Tanaka, H. Takahashi, & A. Amemural, "Transcription of the principal sigma‐factor genes, rpod and rpos, in pseudomonas aeruginosa is controlled according to the growth phase", Molecular Microbiology, vol. 13, no. 6, p. 1071-1077, 1994. https://doi.org/10.1111/j.1365-2958.1994.tb00498.x
