Dissociation and reassociation of poliovirus. II. Protein components obtained by urea treatment of the virus particle.

Dissociation of poliovirus by 9 M urea in 0.015 M NaCl at 25 degrees C resulted in the liberation of 35S RNA and of polypeptides sedimenting at 2S in sucrose gradients containing 9 M urea. However, a ribonucleopolypeptide (RNPP) complex sedimenting at 45S and oligomers of the viral polypeptides sedimenting at 7--8S were found in addition to the monomers sedimenting at 2S when the urea concentration was lowered to 5 M after the dissociation procedure. Ribonuclease treatment prevents the appearance of the RNPP-complex. The amount of the RNPP-complex decreased, when the dissociation was performed at higher ionic strength. Under these conditions small amounts of empty capsids were detected. Polyacrylamide gel electrophoresis showed that the RNPP-complex contained the polypeptide VP1. The oligomers (7--8S) contained the polypeptide VP3 and small amounts of VP2. The bulk of VP2 and some VP3 were found in the 2S position together with VP4. The molecular weight of the dissociation products in urea and phosphate buffer was determined by gel filtration to be about 30,000 for the monomeric polypeptides containing predominantly VP2 and about 70,000 for the oligomeric polypeptides containing predominantly VP3. Our results demonstrate that the oligomers and the RNPP-complex are not primary products obtained by dissociation of the virus particle by urea but are due to a reassociation of the polypeptides or of VP1 and RNA.