STRESS ACTIVATION OF BACILLUS-SUBTILIS SIGMA(B) CAN OCCUR IN THE ABSENCE OF THE SIGMA(B) NEGATIVE REGULATOR RSBX

Environmental stress activates sigma(B), the general stress response s igma factor of Bacillus subtilis, by a pathway that is negatively cont rolled by the RsbX protein. To determine whether stress activation of sigma(B) occurs by a direct effect of stress on RsbX, we constructed B . subtilis strains which synthesized various amounts of RsbX or lacked RsbX entirely and subjected these strains to ethanol stress. Based on the induction of a sigma(B)-dependent promoter, stress activation of sigma(B) can occur in the absence of RsbX. Higher levels of RsbX faile d to detectably influence stress induction, but reduced levels of RsbX resulted in greater and longer-lived sigma(B) activation. The data su ggest that RsbX is not a direct participant in the sigma(B) stress ind uction process but rather serves as a device to limit the magnitude of the stress response.