Mutational analysis of F-pilin reveals domains for pilus assembly, phage infection and DNA transfer.

The F-pilus has been implicated in recipient cell recognition during the establishment of a stable mating pair before conjugation as well as forming part of the conjugative pore for DNA transfer. The F-pilus is the site of attachment of the filamentous phages (M13, f1 and fd), which attach to the F-pilus tip, and the RNA phages, R17 and Qbeta, which attach to different sites exposed on the sides of the pilus. R17 has been shown to undergo eclipse, or capsid release, outside the cell on pili attached to cells. New and existing mutants of traA combined with natural variants of F-pilin were assayed for pilin stability and processing, pilus elongation, transfer, phage sensitivity and R17 eclipse. Phenotypes of these mutants indicated that the F-pilin subunit contains specific regions that can be associated with pilus assembly, phage sensitivity and DNA transport. Mutations involving lysines and phenylalanines within residues 45-60 suggest that these residues might participate in transmitting a signal down the length of the pilus that initiates DNA transfer or R17 eclipse.