Effect of beta-decay of radionuclides incorporated into influenza virus RNA and proteins on the infectivity of the virus and antigenicity of its nucleoprotein.

The effect of beta-decay of radionuclides incorporated into influenza virus on the properties of the two closely adjacent structures--RNA and nucleoprotein (NP)--was studied. The long-term storage of 3H-uridine labelled influenza virus was shown to lead to the loss of infectivity. This effect may be explained by lethal intra-molecular modifications of viral RNA, caused by beta-decay of 3H incorporated into the molecule. There was an accompanying decrease of monoclonal antibody (MAB) binding activity, this also being a plausible result of beta-decay. The different rates of inactivation of MAB binding activity of different epitopes of NP of the 3H-labelled virus shown in our studies suggest that there are different types of structural organization or different location of these epitopes in the NP. The effect of 3H-decay on the intracellular RNA of reproducing virus lead to a decrease in virus yield; this may be due to radiation- and transmutation-induced damage of messenger and progeny RNA populations synthesized during the infection. The storage of influenza virus labelled with 14C-aminoacids lead to a decrease in MAB binding activity of the NP that was unaccompanied by a decrease in infectivity. Furthermore, 14C-decay in proteins of reproducing virus had no adverse effect.

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.

DNA sequences in influenza virions.

During the propagation of A (H3N2) influenza virus in chick embryos, incorporation of 3H-thymidine into virions takes place, whereas no such incorporation occurs with Newcastle disease virus. Incorporation of 3H-thymidine is a result of DNA synthesis. This virion-associated DNA is present in cores obtained after treatment of virions with bromelain.