A key translational regulator that binds mRNA to regulate translation initiation and/or mRNA stability. Mediates global changes in gene expression, shifting from rapid growth to stress survival by linking envelope stress, the stringent response and the catabolite repression systems. Usually binds in the 5'-UTR; binding at or near the Shine-Dalgarno sequence prevents ribosome-binding, repressing translation, binding elsewhere in the 5'-UTR can activate translation and/or stabilize the mRNA. Its function is antagonized by small RNA(s). Binds to mRNA to regulate gene activity at a post-transcriptional level (Probable). Represses expression of many toxic extracellular enzymes and compounds; decreases translation of lasI and rhlI (PubMed:11673439). Positively controls swarming motility and rhanolipid and lipase, possibly via expression of rhlA; activates transcription of the CsrA/RsmA antagonistic sRNA RsmZ (PubMed:15126453). Overexpression dramatically reduces extracellular protease, elastase (lasB) and staphyolytic (lasA) activities, decreases HCN production, decreases levels of autoinducers 3-oxo-C12-HSL (3-oxo-N-(tetrahydro-2-oxo-3-furanyl)-dodecanamide) and C4-HSL (N-butanoylhomoserine lactone), and abolishes production of cytotoxic internal lectin PA-IL (lecA) (PubMed:11673439). Control of hcn expression is post-transcriptional (PubMed:11673439). Replaces endogenous gene(s) in E.coli and P.fluorescens (PubMed:16359708). Probably binds to and is sequestered by non-coding small RNA (sRNA) RsmZ; overexpression of rsmZ produces very similar phenotypes to deletion of rsmA, while rsmZ deletion has no phenotype (PubMed:15126453). Homodimer; the beta-strands of each monomer intercalate to form a hydrophobic core while the alpha-helices form wings that extend away from the core (PubMed:16104018). Low levels of expression in early log phase, increases about 3-fold by stationary phase (at protein level) (PubMed:11673439). Grows slightly more slowly; 30% reduction in staphylolytic activity, increased production of lectin PA-IL, blue-green pigment pyocyanine and HCN (PubMed:11673439). Increases levels of autoinducers 3-oxo-C12-HSL (3-oxo-N-(tetrahydro-2-oxo-3-furanyl)-dodecanamide) and C4-HSL (N-butanoylhomoserine lactone) in early log phase which becomes nearly wild-type (3-oxo-C12-HSL) or 2-fold greater (C4-HSL) by late log phase (PubMed:11673439). Loss of swarming mobility and rhamnolipid production, loss of sRNA RsmZ expression, decreased lipase, increases synthesis of pyocyanine and HCN (PubMed:15126453). Loss of swarming mobility, overproduction of pyocyanine, reduction in lipase biosynthesis (PubMed:16359708). Belongs to the CsrA/RsmA family.