Induction of haemolytic activity in Escherichia coli by the slyA gene product

The Salmonella typhimurium protein SlyA(ST), originally described as a cytolysin, shows sequence similarities to several known bacterial regulatory proteins. A homologue to the slyA(ST) gene has been localised to min 37 of the Eschericia coli K-12 chromosome and has been designated slyA(EC). When introduced in trans on a plasmid, the slyA(EC) gene conferred a haemolytic phenotype on wild-type but not clyA-knockout strains of E. coli K-12. The clyA gene encodes a novel haemolysin that is not expressed by wild-type E. coli under tested laboratory conditions. Western and Northern blot analyses, and DNA-band-shift assays support a model whereby the SlyA(EC) protein activates clyA expression by binding to the clyA promoter region, thereby supporting the sequence similarity data in suggesting that SlyA(ST) is a haemolysin activator rather than being a haemolysin per se.