ISOLATION AND CHARACTERIZATION OF A TN5-INDUCED TOLQ MUTANT OF ESCHERICHIA-COLI

Transposon mutagenesis was used to isolate an Escherichia coli mutant that released into the external medium a heterologous protein, the Aer omonas hydrophila aerolysin. Genetic mapping and phenotypic characteri zation of E. coli CM209 showed that Tn5 is inserted in the role gene. This mutant strain released a significant amount of unprocessed (proae rolysin) protein into the external medium, together with other peripla smic proteins. Similar levels of the toxin were detected in the intrac ellular compartments of the parental and mutant strains. Whereas inact ivation of the role gene itself was responsible for some of the phenot ypic properties of strain CM209, such as tolerance to group A colicins or to filamentous bacteriophages, the leaky phenotype was associated with a polar effect exerted by Tn5 on distal genes of the tolQRA clust er.