Characterization of the F plasmid TraJ protein synthesized in F' and Hfr strains of Escherichia coli K-12.

Using purified F plasmid TraJ protein (Cuozzo, M., Silverman, P., and Minkley, E. (1984) J. Biol. Chem. 259, 6659-6666), we prepared rabbit anti-TraJ protein antibodies to analyze for the first time the TraJ protein as it is synthesized in normal F' and Hfr conjugal donor strains. Using affinity-purified antibody, we identified the protein on immuno-overlay blots of whole cell proteins separated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. In contrast to the TraJ protein synthesized in large quantity by heat-induced lambda (traJ) lysogens, the TraJ protein synthesized in normal donor cells was soluble, even after sedimentation at 100,000 X g. The soluble protein was found with the cytoplasmic fraction after separation of cytoplasmic and periplasmic proteins. Velocity sedimentation analysis indicated an S20,w of 3.5 for the single molecular species composed of or including all the TraJ polypeptide in crude extracts. Quantitative analyses showed that conjugal donor strains normally contain 2000-4000 TraJ monomers/cell. However, that level depended on other plasmid and chromosomal genes.