Mass, length, composition and structure of the filamentous bacterial virus fd

Abstract

Determinations by three independent methods gave an average of (14.6 ± 0.6) × 10 6 daltons for the anhydrous mass of the filamentous bacterial virus fd; a determination of the mass per unit length by light scattering of the virus in solution gave 1560 ±60 daltons/Å; and three independent methods show that 12.0±O.2% of the virus mass is from the single-stranded circular DNA molecule. The data give an average axial distance of 3.82 ±0.15 Å between major coat protein subunits (5240 daltons each) for virus in solution. The DNA has an up strand and a down strand within the filament, and an average axial distance of 3.29 ± 0.14 Å between neighbouring nucleotides in a given strand is obtained from the data. There are 2.32 ±0.07 nucleotides per major coat protein subunit and hence each of the nucleotides cannot interact in the same way with subunits of coat protein. The results provide a basis for the interpretation of X-ray diffraction patterns of oriented fibers of the virus. The uncertainties cited above are 95% confidence limits.