The immunological and the biochemical relationships between F-type pyocins and phage KFI, which is cross-reactive with anti-F-type pyocin sera, were studied. The primary structures of six subunit proteins of each pyocin were also compared among three F-type pyocins, pyocin Fl, F2, and F3.
Both anti-pyocin F1 and anti-pyocin F3 sera gave precipitin bands with phage KF1 by Ouchterlony's test, and were found to bind to minor subunit proteins P3 and P6 of the phage, which were separated by SDS-polyacrylamide gel electrophoresis. Electron microscopic studies showed that these sera bound to some loci of the rod part of the phage tail. These results showed that the subunit proteins P3 and P6 carried antigenically common parts to F-type pyocin and that P3 and/or P6 were components of the rod part of the phage KF1. The subunit proteins P3 and P6 of the phage were of the same mobilities in SDS-polyacrylamide gel electrophoresis as those of band 1 and band 5 of F-type pyocins, respectively. Tryptic peptide mapping after iodination with ¹²⁵I also showed a partial homology between P3 and band 1, and between P6 and band 5.
The tryptic peptide mapping of the six subunit proteins of each F-type pyocin showed that the primary structure of subunit protein band 1 was almost the same among these pyocins, and subunit protein bands 2, 3, 5, and 6 showed were similar. Only subunit protein band 4 was different among these pyocins. The difference in the action spectra of pyocin F1, F2, and F3 is probably due to the difference in the primary structure of subunit protein band 4, which is a component of the fiber part.