Kinetics of Synthesis of Influenza Virus Ribonucleoprotein Structures

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Abstract
The synthesis of influenza virus ribonucleoprotein structures (RNP) in infected chick embryo cells was analyzed by polyacrylamide gel electrophoresis in the presence of sodium deoxycholate which resolves the RNP into 5 size classes. A relatively small proportion of total RNP accumulated in the nucleus but free NP protein was found there in large amounts over the period 1.5-4 h post-infection. By 4 h post-infection, all cytoplasmic nucleoprotein (NP) was complexed into RNP structures. At early times, during a 15-min pulse of [35S]methionine, nearly all the newly synthesized NP was incorporated into RNP but by 4 h the majority of pulse-labeled NP was present as free protein. The proportion of free NP:NP in RNP remained constant over the 1.5-4 h post-infection period, indicating that there was a delay before the NP synthesized later in infection was assembled into RNP structures. Individual RNP size classes were predominantly cytoplasmic and accumulated at similar rates but were not produced in equimolar amounts. The rates of synthesis of individual RNP were in general agreement with their rates of accumulation, with the remarkable exception of RNP d (containing RNA 7, the matrix protein gene). This was synthesized nearly 10-fold faster but accumulated at the same rate as the other RNP. Possibly RNP d is more rapidly degraded than the other RNP.

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