TYPE-II PROTEIN SECRETION BY PSEUDOMONAS-AERUGINOSA - GENETIC SUPPRESSION OF A CONDITIONAL MUTATION IN THE PILIN-LIKE COMPONENT XCPT BY THECYTOPLASMIC COMPONENT XCPR

Pseudomonas aeruginosa exports a number of hydrolytic enzymes and toxi ns using the type ii or general secretion pathway, found in a variety of Gram-negative bacteria and requiring the functions of at least 12 g ene products (XcpP-Z and PilD/XcpA in P. aeruginosa). A number of thes e gene products are homologues of components of the type IV pilus biog enesis system, including four proteins, XcpT-W, which are highly simil ar to the pilin subunit in their size, localization and post-translati onal modifications. These proteins, in addition to the pilin subunit, are cleaved and methylated by the PilD/XcpA prepilin peptidase, but th eir interactions with other components of the export apparatus are unc lear. Using a medium developed for the selection of export-proficient P. aeruginosa strains, we have isolated temperature-sensitive mutation s in the xcpT gene and extragenic suppressors for one of the mutants. These suppressors fall into two classes, one that maps outside of the xcpP-Z gene cluster and may define additional cellular functions that are required for export, and a second that maps to the xcpR gene produ ct and indicates a potential protein-protein interaction connecting tw o different cellular compartments and required for the assembly or fun ction of the export apparatus.