Evidence of precursors of defective measles virus

Abstract

Cytoplasmic extracts of Vero cells infected with wild strain Edmonston measles virus were found to contain at least two distinct nucleocapsid species. The two most prominent species of nucleocapsids sedimented at 200S and 110S and contained RNA of molecular weight 6.0×10 6 and 0.6×10 6 daltons respectively. Both species of nucleocapsids had a density of 1.31 g/cm 3 in CsCl. A third species sedimenting at 170S was not present in all experiments and was not characterized in detail. Infection of cells with undiluted-passage virus usually resulted in production of mostly 110S nucleocapsids while both 110S and 200S species were found when diluted-passage virus was used. These results suggest that measles virus may produce distinct classes of defective virus which contain segments of RNA representing as little as 10% of the complete viral genome.