Member of the two-component regulatory system GacA/GacS which controls the expression of secondary metabolites and extracellular products. Acts (probably primarily) by activating expression of CsrA1 and CsrA2 antagonist small RNAs (sRNA) RsmX, RsmY and RsmZ which bind to and prevent translation repression by CsrA1 and CsrA2 (PubMed:11807065, PubMed:14622422, PubMed:15601712, PubMed:16286659). Involved in the regulation of secondary metabolism and in the synthesis of the antifungal factors cyanide, 2,4-diacetylphloroglucinol and pyoluteorin (PubMed:1311842). Involved in synthesis of the autoinducing signal (unrelated to N-acylhomoserine lactones, induces the Gac/Csr cascade) (PubMed:16286659). Exercises positive post-transcriptional control over the hcnABC and aprA genes; acts upstream of CsrA2 (rsmA) (PubMed:10570200). Controls expression of csrA1 (rsmE) and csrA2 (PubMed:15601712). Increases 2-fold from exponential to stationary phase (at protein level). Phosphorylated by GacS (Probable). No longer produces the secondary metabolites diacetylphloroglucinol (Phl) or pyoluteorin (2 antifungals) or HCN (PubMed:1311842). No longer protects tobacco plants from attack by the black root rot-causing fungus Thielaviopsis basicola (PubMed:1311842). 50-fold decrease in expression of hcnA (PubMed:10570200). Greatly decreased expression of genes controlled by this two-component system such as aprA, hcnA, phlA and pltA (PubMed:10570200, PubMed:11807065, PubMed:14622422, PubMed:15601712, PubMed:23635605). Loss of expression of small RNAs (sRNA) RsmX, RsmY and RsmZ (PubMed:14622422, PubMed:16286659). Loss of the autoinducing signal (which is unrelated to N-acylhomoserine lactones and induces the Gac/Csr cascade) (PubMed:16286659). Its deletion is suppressed by overexpression of sRNAs RsmZ, RsmY or by RsmX (PubMed:11807065, PubMed:14622422, PubMed:16286659). Decreased expression of translational regulators CsrA1 (rsmE) and CsrA2 (rsmA) (PubMed:15601712).