The Escherichia coli K-12 F plasmid gene traX is required for acetylation of F pilin.

The Escherichia coli F plasmid gene required for amino-terminal acetylation of F-pilin subunits was identified. Using Western blots (immunoblots), we assayed the reaction of monoclonal antibodies with F-pilin polypeptides in inner membrane preparations from various F mutant strains. It was known that JEL92 recognizes an internal pilin epitope and JEL93 recognizes the acetylated amino-terminal sequence (L.S. Frost, J.S. Lee, D.G. Scraba, and W. Paranchych, J. Bacteriol. 168:192-198, 1986). As expected, neither antibody reacted with inner membranes from F- cells or Flac derivatives that do not synthesize pilin. Mutations that affected the individual activities of F tra genes traA, -B, -C, -D, -E, -F, -G, -H, -I, -J, -K, -L, -M, -N, -P, -R, -U, -V and -W or trb genes trbA, -B, -C, -D, -E, -G, -H, and -I did not prevent JEL92 or JEL93 recognition of membrane pilin. However, Hfr deletion mutants that lacked the most-distal transfer region genes did not express pilin that reacted with JEL93. Nevertheless, all strains that retained traA and traQ did express JEL92-reactive pilin polypeptides. Analysis of strains expressing cloned tra segments showed that traA and traQ suffice for synthesis of JEL92-reactive pilin, but synthesis of JEL93-reactive pilin is additionally dependent on traX. We concluded that the traX product is required for acetylation of F pilin. Interestingly, our data also showed that TraA+ TraQ+ cells synthesize two forms of pilin which migrate at approximately 7 and 8 kDa. In TraX+ cells, both become acetylated and react with JEL93. Preparations of wild-type F-pilus filaments contain both types of subunits.