Defective-Interfering Particles of Semliki Forest Virus: Structural Differences between Standard Virus and Defective-Interfering Particles

Abstract

Serial passaging of Semliki Forest virus in BHK cells at a constant input multiplicity of 50 p.f.u./cell resulted in a 4 log₁₀ drop in the yield of infectious virus by passage 9. An interference analysis showed that this drop was due to the presence of defective-interfering (DI) particles. Attempts were made to separate the DI particles from standard virus by equilibrium and velocity centrifugation. Only equilibrium centrifugation on CsCl resolved the DI particles (identified by interference analyses) from standard virus. The buoyant density of the DI particles (1.23 g/ml) was higher than that of standard virus (ρ = 1·20 g/ml).