Purification of alpha-hemolysin from an overproducing E. coli strain.

The genetic determinant of the alpha-hemolysin encoded by plasmid pHly152 has been cloned in both orientations in plasmid pBR322 giving rise to plasmids pSU157 and pSU158. E. coli strains carrying either of these recombinant Hly plasmids produced about 20 times more hemolysin activity than the parental plasmid pHly152, when grown in minimal medium supplemented with hemoglobin. Thus high hemolytic activity is not lethal to the cells, contrary to previous assumptions. alpha-Hemolysin was purified from culture supernatants of strain SU100 (pSU157) by ammonium sulfate precipitation and gel filtration in Sephacryl S-200 in the presence of 6 M urea. When purified alpha-hemolysin preparations were subjected to electrophoretic analysis in denaturing conditions, a single 107 kdal polypeptide was observed. This probably corresponds to the alpha-hemolysin protein, since an isogenic E. coli strain carrying plasmid pSU161, an Hly- mutant derivative of pSU157, did not synthesize the 107 kdal polypeptide.