Genes and gene products involved in the synthesis of F-pili.

Membrane fractions containing [35-S]methionine labeled proteins synthesized by Flac and Flac tra mutant strains or by lambda tra transducing phages expressed in such strains have been analyzed in order to investigate the pathway for synthesis of the F-pilin subunit and the gene products involved in synthesis of F-pili. Our data indicate that the synthesis of a mature F-pilin subunit requires the expression of at least 2 tra operon genes in addition to the structural gene for F-pilin, traA. In the absence of these activities, traA expression results primarily in the synthesis of a polypeptide, Ap14, with an apparent molecular weight of approximately 14,000. We assume this polypeptide corresponds to the direct product of the traA gene. In the presence of traQ activity, the major detectable product of traA is a polypeptide, Ap7(Q), which migrates with an apparent molecular weight of 7,000, suggesting that traQ product may process or assist in the processing of Ap14. Polypeptide Ap7(Q) is not, however, mature F-pilin, since it reacts poorly with anti-F-pilus-serum. Synthesis of a polypeptide which appears to be antigenically equivalent to F-pilin and which we assume requires a modification of the F-pilin N-terminus, is detected as synthesis of a polypeptide, Ap7*. This protein migrates slightly more slowly than Ap7(Q) on our polyacrylamide gels. Polypeptide Ap7*, can be efficiently precipitated with F-pilus antiserum, and can be detected in both inner membrane and outer membrane fractions under conditions where assembly of F-pili can occur. These data suggest that Ap7* is the mature F-pilin subunit and is assembled from an inner membrane pool. Synthesis of Ap7* appears to require traG activity, but may also be dependent upon additional tra activities.