Synthesis of F-pilin polypeptide in the absence of F traJ product

The products of a lambda transducing phage (ED lambda 101) which carries a segment of the F tra operon expressing F traA , traL , and traE activity from the lambda leftward promoter were examined using a uv-irradiated host system. After infection of an F- host, products of traE (19,500 Da) and traA (14,000 Da) were detectable among the lambda early proteins synthesized. Infection of an Flac host altered the pattern of polypeptides synthesized by the phage in that the 14,000-Da traA product became barely detectable and was replaced by a polypeptide which migrated at 7000 Da. A derivative of ED lambda 101 carrying the traA1 amber mutation was unable to synthesize either the 14,000-Da polypeptide in F- cells or the 7000-Da polypeptide in Flac cells. The 7000-Da polypeptide derived from ED lambda 101 was synthesized in the absence of traJ product in F- cells coinfected with a second transducing phage which carried a tra operon segment including traQ . It was also a product of ED lambda 134 which expresses genes traA through traH . The 7000-Da polypeptide, like F-pilin, associated primarily with the inner membrane, and could be immunoprecipitated with antiserum prepared against purified F-pili. Analysis of membranes from F- cells infected with ED lambda 101 indicated that the 14,000-Da traA product synthesized under these conditions accumulated in the inner membrane. These results show that both the 14,000-Da traA product might be processed to F-pilin in a traQ -dependent reaction which occurs in or on the inner membrane of the Escherichia coli host. However, the possibility that traQ encodes a regulatory product which affects expression of the traA sequence has not been excluded.