A Fibrous DNA Phage (fd) and a Spherical RNA Phage (fr) Specific for Male Strains of E coli

Abstract

The phage fd is a flexible rod with a sedimentation constant of 40 s. From electron microscopic photographs the length of the rod is 7600 A, the diameter 50 A. The diameter calculated from aggregated particles (1430 molecular weight/A) is 46 A. The molecular weight of the phage is probably 11.3 [center dot] 106 10%. The single-stranded deoxyribonucleic acid (DNA) phage fd appears to have the physical form of a closed ring, similar to the filamentous DNA of the phage [PHI]X 174. According to the sedimentation behavior, the fd-DNA has the same size as [PHI]X-DNA (molecular weight 1.6 [center dot] 106). The spherical ribonucleic acid (RNA) phage fr is similar in size to other known RNA phages. The sedimentation constant, S020 w is 79 s. The electron microscopic diameter is 210 A. The molecular weight is about 4.1 [center dot] 106/1 g of phage binds 1.2 g of hydration water. S[image] of fr-RNA in 0.02 [image] citrate at 20[degree]C is 21 s. Determinations in 0.1 [image] NaCl give essentially higher sedimentation rates, apparently because of the coiling of the RNA molecule under the changed conditions increases. The magnitude of the change is noteworthy, since the UV absorption of the fr RNA in the range 0.01 - 0.1 [image] NaCl is practically constant. The molecular weight of the fr RNA from sedimentation and viscosity is 1.3 [center dot] 106. The sedimentation behavior of the light fd particles and the light fr particles is described. The appendix gives a simplified method for the determination of the molecular weight of the small, spherical viruses from the sedimentation rate and the nucleic content of the particles as determined by chemical analysis.