THIOREDOXIN IS AN ESSENTIAL PROTEIN-INDUCED BY MULTIPLE STRESSES IN BACILLUS-SUBTILIS

Thioredoxin, a small, ubiquitous protein which participates in redox r eactions through the reversible oxidation of its active center dithiol to a disulfide, is an essential protein in Bacillus subtilis, Pi vari ety of stresses, including heat or salt stress or ethanol treatment, s trongly enhanced the synthesis of thioredoxin in B. subtilis, The stre ss induction of the monocistronic trxA gene encoding thioredoxin occur s at two promoters. The general stress sigma factor, sigma(B), was req uired for the initiation of transcription at the upstream site, S-B, a nd the promoter preceding the downstream start site, S-A was presumabl y recognized by the vegetative sigma factor, sigma(A) In contrast to t he heat-inducible, sigma(A)-dependent promoters preceding the chaperon e-encoding operons groESL and dnaK, no CIRCE (for controlling inverted repeat of chaperone expression) was present in the vicinity of the st art site, S-A, The induction patterns of the promoters differed, with the upstream promoter displaying the typical stress induction of sigma (B)-dependent promoters. Transcription initiating at S-A, but not at S -B, was also induced after treatment,vith hydrogen peroxide or puromyc in, Such a double central of stress induction at two different promote rs seems to be typical of a subgroup of class In heat shock genes of B . subtilis, like clpC, and it either allows the cells to raise the lev el of the antioxidant thioredoxin after oxidative stress or allows str essed cells to accumulate thioredoxin. These increased levels of thior edoxin might help stressed B. subtilis cells to maintain the native an d reduced state of cellular proteins.