Defective interfering particles of poliovirus. 3. Interference and enrichment

Interference with standard poliovirus growth resulting from co-infection of cells with standard virus and defective interfering particles has been investigated. At all time following infection, co-infected cells produced less standard progeny than cells infected only by standard virus. The total yield of physical particles and the percentage of standard virus among these particles was a linear function of the percentage of standard virus in the inoculum. The actual yield of standard virus thus varied as the square of the percentage of standard virus in the inoculum. The extent of interference could also be controlled by varying the time interval between initial infection of cells by one type of particle and superinfection by the other.Identical amounts of viral RNA and virus-specific polyribosomes are formed in co-infected or singly infected cells. Interference apparently results from the partitioning of these limited synthetic capacities between standard and defective interfering-specific RNA and protein synthesis. Standard and DI RNA appear to serve equally well as messenger RNAs because standard and DI-specific viral proteins are synthesized in ratios proportional to the ratio of standard to DI particles in the inoculum. Only standard RNA can direct the formation of capsid protein, so co-infected cells contain reduced amounts of the virion protein precursor, the procapsid. Standard and DI RNA are encapsidated with approximately equal efficiency. Thus interference results from equal participation in the intracellular events of the infection cycle by both types of particles.The progeny yield from co-infected cells was always enriched about 5 to 8% in DI particles. Progeny were produced in the enriched ratio throughout the infection cycle.