Component of the thioredoxin-thioredoxin reductase system. Participates in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyzes dithiol-disulfide exchange reactions (By similarity). Expressed from 2 promoters, 1 of which (trxCp1) is under control of SigR. Dramatically but transiently induced by the thiol-oxidizing agent diamide. In an rsrA mutant expression is constitutive and uninduced by diamide. Belongs to the thioredoxin family.