Fig. 5.
Schematic of how polysulfides impact SqrR-mediated polysulfide-induced transcription for wild-type cells stressed with Na2S. Exogenous or endogenous sulfide is quickly (t < 2 min) converted to polysulfides via a “housekeeping” or constitutive response as a result of chemical and/or enzymatic processes. The so-generated polysulfides react with SqrR and the repressor activity of SqrR is maintained in an inactive DNA-binding state by tetrasulfide formation (n > 1) between the Cys residues (2 min < t < 30 min). During this time, the expression of genes encoding SQR and the rhodanese (Rhod) are de-repressed and high levels of low molecular weight thiol (LMWT) and proteome persulfides are continuously generated from sulfide via an “inductive response” (t > 30 min). After this time, other more oxidized sulfur species (Sn2–, thiosulfate and sulfate) begin to accumulate, thus reducing cellular [RSSH], restoring unstressed physiology and SqrR-mediated transcriptional repression (t ∼ 120 min).