Extra RNAs of von Magnus particles of influenza virus cause reduction of particular polymerase genes.

Extra RNAs, or RNA species other than eight gene segments, in von Magnus particles of the influenza virus WSN strain were studied by polyacrylamide gel electrophoresis and oligonucleotide mapping. From the original virus stock, various cloned stocks were obtained, each giving rise to a characteristic set of extra RNAs. One cloned virus stock contained a large number of von Magnus particles. The RNA pattern was characterized by two prominent extra RNAs (X1 and X2) and a decrease in the content of two polymerase genes, P1 and P2. Segregation of the two extra RNAs was carried out by coinfection of cells with a von Magnus particle and infectious virions. The results showed that the presence of one of the extra RNAs (X2) was associated with a reduction in the amount of the P1 gene and that the presence of the other extra RNA (X1) was associated with a reduction in the amount of the P2 gene. Oligonucleotide mapping showed that both extra RNAs, X1 and X2, were derived from the P1 gene. The results suggested that an extra RNA did not necessarily cause the reduction of the progenitor polymerase gene, but might cause the reduction of another polymerase gene.