Printed in Great Britain The Structure o f Heated Pol iovirus Particles

Purified poliovirus preparations were heated and analysed by sucrose gradient centrifugation. They consisted of virus-like particles containing RNA and sedi-menting at about 8os, empty 8o s capsids, 35s virus RNA, and a non-sedimentable capsid polypeptide (VP 4)- By electron microscopy the 8os ribonucleoprotein particles (8os RNP)were similar in appearance to intact poliovirus particles. They contained infectious, RNase-sensitive RNA that could be liberated from the capsid by treatment at room temperature with 1 % sodium dodecyl sulphate. One of the virus polypeptides was missing, and they had lost the antigenicity of the mature virus and the ability to adsorb to HeLa cells. Degradation of poliovirus particles probably occurs in two steps: the first is the splitting off of a minor part of the capsid protein (VP 4) followed under certain conditions by a liberation of the RNA from the capsid. The alteration of the physical and biological properties of the virus particle is probably due to the loss of the protein rather than to the liberation of the RNA