Identification and transcriptional analysis of new members of the sigma(B)regulon in Bacillus subtilis

Bacillus subtilis responds to various stimuli (heat, ethanol and salt stres s, energy starvation) with the induction of general stress proteins (GSPs). Most of them belong to the stress and stationary-phase regulon controlled by the alternative sigma factor sigma(B). The majority of sigma(B)-dependen t proteins are thought to provide a precautionary general stress resistance in stressed or starved cells. In this report, the identification and trans criptional analysis of nine new members of the sigma(B) regulon are describ ed. The biochemical function was not determined for any of the proteins enc oded by the nine new sigma(B)-dependent stress genes, however, similarities to proteins in the databases allowed a distinction between proteins with p utative (i-iv) and unknown (v) function. The putative functions of BmrU, Yc dF, YdaD, YdaP, YhdN and YocK underline the suggested protective role of si gma(B)-dependent GSPs and also elucidate new areas where sigma(B) might pla y an important role. (i) The finding that the bmrUR operon is under sigma(B ) control indicates that the elimination of multidrug compounds might be a new function in multiple stress resistance. (ii) YcdF and YdaD resemble NAD (P)-dependent dehydrogenases. Both proteins could be involved in the genera tion of NAD(P)H and therefore in the maintenance of the intracellular redox balance under stress. (iii) The ydaP gene might belong to the increasing n umber of sigma(B)-dependent genes whose orthologues are under the control o f sigma(S) in Escherichia coli, indicating that both regulons may fulfil si milar functions. (iv) YhdN shows weak similarities to potassium ion channel proteins and YocK shows resemblance to the DnaK suppressor protein DksA. ( v) Three new sigma(B)-dependent genes (ydaE, ydaG and yfkM) encoding protei ns with still unknown functions were also described. Further analyses of co rresponding mutants might allow a first prediction of their function within the framework of the general stress regulon.