GROUPING OF RNA COLIPHAGES BASED ON ANALYSIS OF THE SIZES OF THEIR RNAS AND PROTEINS

In order to elucidate the intergroup relationships among four groups of RNA coliphages (RNA phages), we studied the sizes of their RNAs by measuring the sedimentation velocity of the RNA in a sucrose density gradient and the electrophoretic mobility of the RNA and those of proteins in polyacrylamide gel. The RNAs of group I, II, III, and IV phages (including serological intermediates) were found to have sedimentation coefficients of 24, 23, 27, and 28 S by sucrose density gradient centrifugation analysis and to have average molecular weights of 1.21, 1.20, 1.39, and 1.42 × 106 daltons by gel electrophoretic analysis, respectively. In the virions of group I and II phages, there were two kinds of protein (maturation protein and coat protein). In those of group III and IV phages, an additional protein, read-through (IIb or Al) protein (average molecular weights: 3.85 × 104 for group III, and 3.90 × 104 for group IV phages) was detected. The average molecular weights of coat protein from groups I, II, III, and IV were 1.40, 1.29, 1.69, and 1.73 × 104, respectively. Those of maturation protein were 4.48, 4.45, 4.50, and 4.8 × 104, respectively. Read-through protein was synthesized not only in cells infected with group III and IV phages, but also in a cell-free protein synthesizing system directed by groups III and IV phage RNAs. These results indicate that a distinct difference (about 20%) in molecular size of RNA exists between groups I and II and groups III and IV, which reflects the presence of readthrough protein in groups III and IV. The above results suggest that the molecular sizes of RNAs and virion proteins may offer a useful means for grouping RNA phages, because the present results were in good agreement with those of grouping of RNA phages based on serological property. In this respect, the serologically intermediate phages, JP34 and MX1, were classified into groups II and IV, respectively. © 1979.