Location of F plasmid transfer operon genes traC and traW and identification of the traW product

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Abstract
As part of an analysis of the conjugative transfer genes associated with the expression of F pili by plasmid F, we have investigated the physical location of the traC and traW genes. We found that plasmid clones carrying a 2.95-kilobase EcoRI-EcoRV F transfer operon fragment were able to complement transfer of F lac traC mutants and expressed an approximately 92,000-dalton product that comigrates with TraC. We also found that traW-complementing activity was expressed from plasmids carrying a 900-base-pair SmaI-HincII fragment. The traW product was identified as an approximately 23,000-dalton protein. The two different F DNA fragments that expressed traC and traW activities do not overlap. Our data indicate that the traC gene is located in a more-tra operon promoter-proximal position than suggested on earlier maps and that traW is distal to traC. These results resolve a long-standing question concerning the relationship of traW to traC. The clones we have constructed are expected to be useful in elucidating the role of proteins TraC and TraW in F-pilus assembly.