PROTEASE ACTIVITY OF OUTER-MEMBRANE PROTEIN OMPT IN CLINICAL ESCHERICHIA-COLI ISOLATES - STUDIES USING TRANSLATION INITIATION-FACTOR IF2 ASTARGET PROTEIN

During purification of the translation initiation factor IF2 from ompT (+) strains of Escherichia coil the IF2 is partially degraded in the p resence of membrane debris during the first steps of purification. Thi s is a result of proteolytic cleavage by outer membrane protease OmpT [1]. Here we have investigated the activity of OmpT in 51 clinical E. coil isolates of human origin, by a time dependent OmpT activity assay using IF2 as target protein. The activity of OmpT in the outer cell m embrane is highly variable among wild type E.coli strains, ranging fro m no detectable activity in 65% of the strains to a very high activity in 5 strains (10%). The OmpT activity is closely related to the assay temperature and to the growth temperature of the cells, and can be re duced or even eliminated by lowering the temperature of growth. The re sults open the possibility of using non-denaturing gel electrophoresis of crude cell lysates as a screening method in population genetic stu dies of initiation factor IF2 and other cytoplasmic proteins which are cleaved by OmpT.