Function
A translational regulator that binds mRNA to regulate translation initiation and/or mRNA stability (PubMed:17704818, PubMed:23635605). Post-transcriptionally represses the expression of genes controlled by GacA/GacS (PubMed:15601712, PubMed:23635605). Binds the 5' UTR of mRNA; the mRNA binds to the outside edge to each monomer and each dimer could bind the same mRNA twice (PubMed:17704818). Recognizes a (A/U)CANGGANG(U/A) consensus, binds to GGA (part of the Shine-Dalgarno sequence) in the 5' UTR loop, which prevents ribosome binding (PubMed:17704818, PubMed:24561806, PubMed:23635605). Overexpression represses target protein expression; mutating nucleotides in the 5' UTR abolishes repression in vivo (PubMed:17704818, PubMed:23635605). Binds specifically to small RNAs (sRNA) RsmX, RsmZ and RsmY; these sRNAs fold into secondary structures with multiple GGA sequences in loops to which the CsrA proteins bind (PubMed:15601712, PubMed:16286659, PubMed:24828038). Binding to RsmX, RsmY or RsmZ titrates the protein so that it can no longer bind mRNA and repress translation (PubMed:15601712, PubMed:24828038). RsmZ can bind up to 5 CsrA1 (rsmE) dimers; they bind cooperatively to GGA sequences in RsmZ in a defined order (PubMed:24828038, PubMed:24561806). Required for optimal expression and stability of sRNAs RsmX, RsmY and RsmZ (PubMed:15601712, PubMed:16286659). Four CsrA1 dimers maximally protect RsmZ from RNase activity (PubMed:24828038). Deletion of rsmX, rsmY or rsmZ alone has no detectable phenotype, but a double rsmY-rsmZ deletion has a marked decrease in production of secondary metabolites HCN, exoprotease AprA, antifungal agent 2,4-diacetylphloroglucinol and swarming motility, and protects cucumber plants from fungal infection less well than wild-type; the triple sRNA deletion has even stronger loss of these phenotypes (PubMed:16286659).