Bacterial expression of human respiratory syncytial viral phosphoprotein P and identification of Ser237 as the site of phosphorylation by cellular casein kinase II.

The phosphoprotein P gene of human respiratory syncytial virus has been cloned and the protein expressed in Escherichia coli. The expressed protein was soluble, unphosphorylated, and constituted approximately 10% of the total bacterial protein. Electrophoretic and antigenic analyses demonstrated the identity of the recombinant protein with viral P protein and P protein synthesized in reticulocyte lysates. Purified recombinant P protein was efficiently phosphorylated in vitro by purified native as well as recombinant casein kinase II (CKII) or by the CKII activity in uninfected cell extracts. Through deletions and site-directed mutagenesis, the site of CKII phosphorylation was mapped to a single serine residue (Ser237) near the C-terminal end of the P protein.