Azotobacter phages: Properties of phages A12, A21, A31, A41 and their constituent DNAs

The properties of several Azotobacter vinelandii phages and of the DNA isolated from each have been investigated. Phages A12, A21, and A41 have short noncontractile tails. A12 and A21 have virion weights of 80 × 10 6 daltons and contain 58% DNA. A31 has a long noncontractile tail, a virion weight of 175 × 10 6 daltons and contains 26% DNA. A31 and A41 are unstable in salt solutions of moderate ionic strength. All phages contain linear, double-stranded DNA that sediments as a single component in neutral and alkaline solutions. The molecular weights of A12, A21, and A31 DNAs obtained by equilibrium density gradient sedimentation are (46 ± 7) × 10 6, (42 ± 5) × 10 6 and (47 ± 5) × 10 6, respectively. Electron microscope length measurements using the replicative form of ∅X174 DNA as an internal contour length standard yielded molecular weights of (44.3 ± 2) × 10 6, (45.6 ± 1.2) × 10 6 and (46.5 ± 2.6) × 10 6, respectively. The buoyant densities of A12 and A21 DNA in CsCl and Cs 2SO 4 indicate a G + C content of 58% consistent with the T m . For A31 DNA the buoyant densities suggest a G + C content of 52% whereas the T m corresponds to 69% G + C. A12 and A21 DNAs show strand separation in an alkaline CsCl gradient (Δ ρ⋍0.006 g ml −1).