An X‐Ray Small Angle Study of the Bacteriophages fr and R17

Abstract

X‐ray small angle scattering was performed on solutions of the bacteriophages fr and R17. The scattering curves of the phages are nearly identical. The radius of gyration was found to be 105.2 Å, the molecular weight as obtained from a high precision measurement is 3.62 × 10 6 . The radial excess electron density distribution, derived from measurements in 0.02 M Tris‐Cl buffer pH 7.2 containing 0.15 M NaCl and 1 mM EDTA, indicates that the phages have a mean outer radius of 131.7 Å and consist of a shell and a less dense core. The core consists of RNA as is shown by measurements in sucrose solutions. It contains only about 80% of the RNA, the remaining 20% are considered to penetrate into the shell. Models calculated assuming the mean outer radius of the RNA to be 107.8 Å yield a mean inner radius of the protein shell of 104.9 Å. The amount of water associated with the phages is found to be about 0.9 g/g.