Control of extracellular polysaccharide synthesis in Erwinia stewartii and Escherichia coli K-12: a common regulatory function.

Aprimary determinant ofpathogenicity inErwinia stewartii istheproduction ofextracellular polysaccharide (EPS). A single mutation canabolish bothEPSsynthesis andpathogenicity; bothproperties arerestored bya single cosmid clone. Subcloning andinsertion analysis havedefined asingle positive regulatory function which shares anumberofsimilarities withthercsAfunction ofEscherichia coli K-12, apositive regulator forcapsular polysaccharide synthesis. InE.stewartii, thegenepromotes thetranscription ofatleast twooperons(cps) involved inEPSsynthesis; we havepreviously demonstrated a similar function forrcsAinE.coli. Bothgenes codeforproteins of25to27kilodaltons; bothproteins areunstable inE.coli. TheE.stewartii RcsAprotein was stabilized inE.coli lonmutants, as theRcsAproduct fromE.coli is.TheE.stewartii function complemented E.coli rcsAmutants, andtheE.coli RcsAfunction increased cps expression andrestored virulence inE.stewartii mutants. Therefore, these twogram-negative organisms share a similar componentof their regulatory circuitry forthecontrol ofcapsular polysaccharide synthesis.