Phosphorylation of tick-borne encephalitis virus NS5 protein

The largest tick-borne encephalitis virus (TBEV) non-structural protein NS5 (100 kDa) is believed to be involved in RNA replication. The protein is phosphorylated in infected cell extracts in the presence of [γ-32P]ATP, as shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis using monoclonal antibodies raised against TBEV NS5 protein. Radioactive labeling of NS5 in cellular extracts at an early stage post-infection is higher than at 24 h post-infection. Incubation of immunoprecipitates of NS5 protein with [γ-32P]ATP in the presence of Mg2+ resulted in the phosphorylation of TBEV NS5 protein and of immunoglobulins. Phosphoamino acid analysis demonstrated that NS5 contains phosphoserine, but not phosphothreonine, or phosphotyrosine.