Dissociation and Reassociation of Poliovirus I. Effect of Urea on the Virion

Abstract

Poliovirus is dissociated by urea in the presence of mercaptoethanol or dithiothreitol into RNA and protein (s). Differences exist in the sensitivity of poliovirus type I, II or III toward these agents. The decrease in infectivity titer of the virion is in the range of 10⁹. After appropriate dis­ sociation no infectious virions are found in urea-treated poliovirus concentrates. The released viral RNA is infectious. Its infectivity (1 × 10⁶ PFU/μg RNA) is comparable to that of phenol extracted RNA. Therefore, urea dissociation is a fast and reliable method for the preparation of infectious poliovirus RNA even at the microliter scale. The dissociation of poliovirus is dependent upon the urea concentration, temperature and pH. The decrease in virion infectivity is time dependent. It is preceded by a lag phase of different lengths for poliovirus type I, II or III. During the lag phase the virion undergoes configurational changes without losing infectivity. From the observed hyperchromic effect it is obvious that the secondary structure of the RNA inside the virion breaks down, giving rise to expanded forms of poliovirus particles. After the lag phase the RNA is released and the empty capsid dissociated into the appropriate polypetides.