Differences in the physical properties of dense and standard poliovirus particles

Dense poliovirus particles (DP) differ in buoyant density, sedimentation coefficient and lability from standard poliovirus particles. Dense particles band at a density of 1-44 g/ml in isopycnic CsCl gradients and sediment in sucrose gradients at 220S. However, when DP are centrifuged in sucrose gradients containing 1-5 M-KCl, NaCl or LiCl, two types of particles are observed, one sedimenting at 220S and the other at 160S. Particles sedimenting at 220S are converted into particles sedimenting at 160S by incubation at 37 degrees C in 1-5 M-KCl. The high buoyant density seems to be correlated with the high lability of DP. Dense particles are extremely labile in isotonic phosphate-buffered saline. Their degradation proceeds through an RNA-containing particle lacking polypeptide VP4, to RNA and empty capsids.