Isolation and Characterization of Bacillus subtilis sigB Operon Mutations That Suppress the Loss of the Negative Regulator RsbX

AUTOR(ES)

Smirnova, Natalya

FONTE

American Society for Microbiology

RESUMO

ςB, a transcription factor that controls the Bacillus subtilis general stress response regulon, is activated by either a drop in intracellular ATP or exposure to environmental stress. RsbX, one of seven ςB regulators (Rsb proteins) whose genes are cotranscribed with ςB, is a negative regulator in the stress-dependent activation pathway. To better define the interactions that take place among the Rsb proteins, we analyzed sigB operon mutations which suppress the high-level ςB activity that normally accompanies the loss of RsbX. Each of these mutations was in one of three genes (rsbT, -U, and -V) which encode positive regulators of ςB, and they all defined amino acid changes which either compromised the activities of the mutant Rsbs or affected their ability to accumulate. ςB activity remained inducible by ethanol in several of the RsbX− suppressor strains. This finding supports the notion that RsbX is not needed as the target for ςB activation by at least some stresses. ςB activity in several RsbX− strains with suppressor mutations in rsbT or -U was high during growth and underwent a continued, rather than a transient, increase following stress. Thus, RsbX is likely responsible for maintaining low ςB activity during balanced growth and for reestablishing ςB activity at prestress levels following induction. Although RsbX likely participates in limiting the ςB induction response, a second mechanism for curtailing unrestricted ςB activation was suggested by the ςB induction profile in two suppressor strains with mutations in rsbV. ςB activity in these mutants was stress inducible but transient, even in the absence of RsbX.

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