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 I'44 g/ml in isopycnic CsC1 gradients and sediment in sucrose gradients at 22oS. However, when DP are centrifuged in sucrose gradients containing 1.5 M-KCI, NaCI or LiC1, two types of particles are observed, one sedimenting at z2oS and the other at I6oS. Particles sedimenting at 2zoS are converted into particles sedimenting at I6oS by incubation at 37°C in P5 M-KC1. 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.