HEAT-SHOCK AND GENERAL STRESS-RESPONSE IN BACILLUS-SUBTILIS

The induction of stress proteins is an important component of the adap tional network of a non-growing cell of Bacillus subtilis, A diverse r ange of stresses such as heat shock, salt stress, ethanol, starvation for oxygen or nutrients etc. induce the same set of proteins, called g eneral stress proteins, Although the adaptive functions of these prote ins are largely unknown, they are proposed to provide general and rath er non-specific protection of the cell under these adverse conditions, In addition to these non-specific general stress proteins, all extrac ellular signals induce a set of specific stress proteins that may conf er specific protection against a particular stress factor, In B. subti lis at least three different classes of heat-inducible genes can be de fined by their common regulatory characteristics: Class I genes, as ex emplified by the dnaK and groE operons, are most efficiently induced b y heat stress, Their. expression involves a sigma(A)-dependent promote r, an inverted repeat (called the CIRCE element) highly conserved amon g eubacteria, and probably a repressor interacting with the CIRCE elem ent, The majority of general stress genes (class II, more than 40) are induced at sigma(B)-dependent promoters by different growth-inhibitin g conditions, The activation of ae by stress or starvation is the cruc ial event in the induction of this large stress regulon, Only a few ge nes, including lon, clpC, clpP, and ftsH, can respond to different str ess factors independently of sigma(B) or CIRCE (class III), Stress ind uction of these genes occurs at promoters presumably recognized by sig ma(A) and probably involves additional regulatory elements which remai n to be defined.