Purification and Some Properties of Bacteriophage ST-1

Abstract

Bacteriophage ST-1 is shown to be a small, isometric, single-stranded deoxyribonucleic acid (SS-DNA) virus with a diameter of about 260 nm. Standard methods for growth, assay, preparation of high-titer lysates, and purification of the phage are suggested. ST-1 infects K-12 and not C strains of Escherichia coli and requires a divalent cation to adsorb to susceptible bacteria. Adsorption also requires an activation of the particle brought on by incubation at 37 C. The latent and eclipse periods are essentially identical (9 to 11 min) in ST-1 infections, with an average burst size about 250 phages per cell. Multiple densities of ST-1 infectivity are observed during purification in CsCl gradients. The virus recovered from different densities has the same sedimentation coefficient and, therefore, all phage containing fractions are pooled during purification. The purified ST-1 particle has a sedimentation coefficient of 121 S relative to φX-174 (114 S ) in a sucrose gradient and a molecular weight of 6.8 × 10 6 (as estimated from its relative sedimentation). The nucleic acid is assumed to be SS-DNA on the basis of (i) the specific incorporation of 3 H-thymine, (ii) the dependence of its UV absorption on temperature, and (iii) its reaction with formaldehyde. ST-1 SS-DNA sediments at 24.4 S relative to φX-174 SS-DNA (23.8 S ).