The ability of Vibrio cholerae to efficiently and selectively secrete cholera toxin represents a remarkable biological process and serves as a paradigm for understanding protein translocation events in bacteria. Cholera toxin is exported to the medium by a two step process which involves crossing the outer membrane as a fully folded protein.The aim of the project is to identify and characterize genes of the toxin secretion apparatus. Some genes involved in the process are homologues of genes in the pul system, found in other Gram-negative bacteria. However, evidence has been obtained that a second translocation machinery is involved. The interactions between the toxin and the proteins of the secretory machinary will be studied, with a focus on the putative outer membrane pore. Comparation between different proteins exported by Vibrio cholerae will be made to determine the similarities in secretion and to identify a secretion signal for translocaiion.