Activation of Bacillus subtilis transcription factor sigma B by a regulatory pathway responsive to stationary-phase signals

Abstract

Alternative transcription factor sigma B of Bacillus subtilis controls a stationary-phase regulon induced under growth conditions that do not favor sporulation. Little is known about the metabolic signals and protein factors regulating the activity of sigma B. The operon containing the sigma B structural gene has the gene order orfV-orfW-sigB-rsbX, and operon expression is autoregulated positively by sigma B and negatively by the rsbX product (rsbX = regulator of sigma B). To establish the roles of the orfV and orfW products, orfV and orfW null and missense mutations were constructed and tested for their effects on expression of the sigma B-dependent genes ctc and csbA. These mutations were tested in two contexts: in the first, the sigB operon was under control of its wild-type, sigma B-dependent promoter, and in the second, the sigB operon promoter was replaced by the inducible Pspac promoter. The principal findings are that (i) the orfV (now called rsbV) product is a positive regulator of sigma B-dependent gene expression; (ii) the orfW (now called rsbW) product is a negative regultor of such expression; (iii) sigma B is inactive during logarithmic growth unless the rsbW product is absent; (iv) the rsbX, rsbV, and rsbW products have a hierarchical order of action; and (v) both the rsbV and rsbW products appear to regulate sigma B activity posttranslationally. There are likely to be at least two routes by which information can enter the system to regulate sigma B: via the rsbX product, and via the rsbV and rsbW products.

Four additional genes in the sigB operon of Bacillus subtilis that control activity of the general stress factor sigma B in response to environmental signals

“…This operon is transcribed from a B -dependent promoter and has the gene order rsbV-rsbW-sigB-rsbX (29). Genetic analysis has shown that the RsbW protein is a key negative regulator responsible for rendering B inactive during logarithmic growth (8). Subsequent biochemical analysis has shown that RsbW is an antifactor that binds directly to B and controls its activity by preventing its association with the RNA polymerase core enzyme (3).…”

“…Significantly, recent work has shown that B is also activated in logarithmically growing cells by a variety of environmental stresses that limit growth, including hyperosmosis, heat, oxidative stress, and ethanol shock (4, 6, 51). These findings have led to the proposal that B controls a general stress regulon (6).Some signals of environmental stress are conveyed to B by a regulatory network encoded by the three genes adjacent to the B structural gene in the sigB operon (2,6,8). This operon is transcribed from a B -dependent promoter and has the gene order rsbV-rsbW-sigB-rsbX (29).…”

“…Subsequent biochemical analysis has shown that RsbW is an antifactor that binds directly to B and controls its activity by preventing its association with the RNA polymerase core enzyme (3). The RsbV protein counters the effect of RsbW and thus acts as a positive regulator that is normally required for B activity to appear in stationary phase, or during logarithmic growth in response to salt or ethanol stress (2,6,8,13). The role of the RsbX negative regulator is less well understood, but genetic analysis indicates that it acts before the RsbV-RsbW pair in a regulatory hierarchy (2,8,24,29).…”

“…The RsbV protein counters the effect of RsbW and thus acts as a positive regulator that is normally required for B activity to appear in stationary phase, or during logarithmic growth in response to salt or ethanol stress (2,6,8,13). The role of the RsbX negative regulator is less well understood, but genetic analysis indicates that it acts before the RsbV-RsbW pair in a regulatory hierarchy (2,8,24,29).During characterization of the RsbV-RsbW-RsbX hierarchy, it became evident that none of the known regulators of B activity was sufficient to fully account for the enhanced stationary-phase activation of B in response to glucose, suggesting that additional regulatory elements remained to be discovered (8). We earlier presented evidence that a second, B -independent promoter must exist for the sigB operon and that this promoter must lie more than 1,100 bp upstream from the B -dependent promoter immediately preceding rsbV (29).…”

“…Some signals of environmental stress are conveyed to B by a regulatory network encoded by the three genes adjacent to the B structural gene in the sigB operon (2,6,8). This operon is transcribed from a B -dependent promoter and has the gene order rsbV-rsbW-sigB-rsbX (29).…”