Defective interfering passages of Sindbis virus: chemical composition, biological activity, and mode of interference.

Defective interfering (DI) particles of Sindbis virus, appearing between the eighth and fourteenth passages, cosediment with and have the same buoyant density as standard virus. Virion RNA from such late passages is heterogeneous by polyacrylamide gel electrophoresis, whereas early passage RNA is homogeneous. No differences were found in the virion proteins from such passages. Cells co-infected with early and late passage virus synthesize as much intracellular viral-specific RNA and protein as is made after infection with early passage virus alone, although virus production is inhibited by 90% or more. Such cells synthesize two new intracellular species of RNA with molecular weights of 2.2 x 10(6) and 0.86 x 10(6). Nucleocapsid assembly is blocked in these cells, and the amount of intracellular capsid protein made is reduced by 50%. The presence of a new intracellular protein in late passage infection was detected by polyacrylamide gel electrophoresis.