Phosphorylation of influenza virus nucleoprotein in vivo.

Two-dimensional analysis of polypeptides from A/FPV/Rostock/34 (FP/R)-infected chick embryos fibroblast cells using non-equilibrium pH gradient gel electrophoresis followed by polyacrylamide gel electrophoresis, showed that nucleoprotein (NP) was the only detectable virus phosphoprotein and was present in both the nucleus and cytoplasm. The kinetics of accumulation of phosphorylated NP in the nucleus and cytoplasm were similar, suggesting that the presence or absence of phosphate groups did not control the entry of NP into the nucleus. In the course of this study, two-dimensional analysis of [35S]methionine-labelled FP/R-infected cells revealed some major differences from previously published work which are discussed.