FIG 4.

Construction and expression of P proteins containing amino acid substitutions. (A) Schematic representation of different substitutions of potential P protein phosphorylation sites. Newly identified and previously reported phosphorylation sites were replaced with alanine residues individually or in combinations as shown. (B) WT and mutant P proteins were expressed under the control of the T7 promoter in BHK21 cells infected with vTF7-3 prior to transfection. Proteins were metabolically labeled with [³⁵S]methionine-cysteine and then immunoprecipitated (IP) with monospecific polyclonal P antibody.