Gradual changes of influenza virions during passage of undiluted material.

Defective influenza virions undergo gradual changes during passage of undiluted material: the amount of RNA in virions diminishes, the equimolarity of the RNA segments is lost and the interfering activity of defective virions decreases. Defective virions of early passages have a small deficiency in genetic material and at a high m.o.i. induce the synthesis of the complete set of virus-specific proteins. Defective virions from later passages are characterized by a considerable deficiency in genetic material and a decrease in the amount of high mol. wt. RNA segments. They do not demonstrate complementation and at a high m.o.i. do not induce the synthesis of virus-specific proteins, thus revealing analogous defects in the genome of the majority of defective virions. The characteristics of protein synthesis in cells infected with these virions are similar to those in uninfected cells. During undiluted passage of influenza virus the cyclic production of defective and infectious virions takes place.