COLICIN-A AND THE TOL PROTEINS INVOLVED IN ITS TRANSLOCATION ARE PREFERENTIALLY LOCATED IN THE CONTACT SITES BETWEEN THE INNER AND OUTER MEMBRANES OF ESCHERICHIA-COLI-CELLS

Colicin A is a bacterial toxin which forms channels in the cytoplasmic membrane of Escherichia coli. Its translocation through the envelope requires the participation of bacterial proteins encoded by the tolQ, -R, -A, and -B genes. Overproduction of the Tol proteins decreased the time needed for colicin A translocation and increased the number of c hannels formed in vivo. Cells overproducing radioactively labeled Tol proteins and containing or not colicin A were fractionated. The Tol pr oteins were mainly recovered in the inner membrane and in the contact sites between the two membranes. The presence of colicin A increased t he specific radioactivity of the Tol proteins in the contact sites. Ou r data suggest that the Tol proteins form a complex of definite stoich iometry in the membranes and that colicin A is associated to this comp lex upon channel formation. We discuss the possibility that the channe l activity determined in vivo is due to the colicin A-Tol proteins com plex.