4 ADDITIONAL GENES IN THE SIGB OPERON OF BACILLUS-SUBTILIS THAT CONTROL ACTIVITY OF THE GENERAL STRESS FACTOR SIGMA(B) IN RESPONSE TO ENVIRONMENTAL SIGNALS

sigma(B) Of the gram-positive bacterium Bacillus subtilis is an altern ative transcription factor activated by a variety of environmental str esses, including the stress imposed upon entry into the stationary gro wth phase. Previous reports have shown that this stationary-phase acti vation is enhanced when cells are grown in rich medium containing gluc ose and glutamine. The sigma(B) structural gene, sigB, lies in an oper on with three other genes whose products have been shown to control si gma(B) activity in response to environmental stress, However, none of these is sufficient to explain the enhanced stationary-phase activatio n of sigma(B) in response to glucose. We show here that the four genes previously identified in the sigB operon constitute the downstream ha lf of an eight;gene operon. The complete sigB operon is preceded by a sigma(A)-like promoter (P-A) and has the order P-A-orfR-orfS-orfT-orfU -P-B-rsbV-rsbW-sigB-rsbX, where rsb stands for regulator of sigma-B an d the previously identified sigma(B)-dependent promoter (P-B) is an in ternal promoter preceding the downstream four-gene cluster. Although t he genes downstream of P-B were also transcribed by polymerase activit y originating at P-A, this transcription into the downstream cluster w as not essential for normal induction of a sigma(B)-dependent ctc-lacZ fusion. However, deletion of all four upstream open reading frames wa s found to interfere with induction of the ctc-lacZ fusion in response to glucose. Additional deletion analysis and complementation studies showed that orfU was required for full glucose induction of sigma(B)-d ependent genes. orfU encodes a trans-acting, positive factor with sign ificant sequence identity to the RsbX negative regulator of sigma(B). On the basis of these results, we rename orfU as rsbU to symbolize the regulatory role of its product.