MEMBRANE TOPOLOGY OF 3 XCP PROTEINS INVOLVED IN EXOPROTEIN TRANSPORT BY PSEUDOMONAS-AERUGINOSA

Xcp proteins constitute the secretory apparatus of Pseudomonas aerugin osa. Deduced amino acid sequence of rep genes, expression, and subcell ular localization revealed unexpected features. Indeed, most Xcp prote ins are found in the cytoplasmic membrane although rep mutations lead to periplasmic accumulation of exoproteins, indicating that the limiti ng step is translocation across the outer membrane. To understand the mechanism by which the machinery functions and the interactions betwee n its components, it is valuable to know their membrane organization. We report data demonstrating the N-in-C-out topologies of three genera l secretion pathway components, the XcpP, -Y, and -Z proteins.