Isolation and characterization of the C and D proteins coded by gene IX and gene VI in the filamentous bacteriophage fl and fd.

The C and D proteins from bacteriophage fd and fl have been purified and characterized. Since the DNA sequence is known, the amino acid composition of these purified proteins indicated that they are coded for by the phage, the C protein being the product of Gene IX and the D protein specified by Gene VI. The molecular weights of the C and D proteins were calculated from the DNA sequences to be 3,650 and 12,350, respectively. These values are close to the molecular weights observed after polyacrylamide gel electrophoresis of the proteins in sodium dodecyl sulfate. Since the C and D proteins can be selectively labeled with radioactive cysteine and arginine, it was possible to estimate the number of the C and D protein molecules relative to the number of A protein molecules which had been accurately determined in previous studies. Based on these results, the average phage particle contains 5 A, 5 D, and 10 C protein molecules.