TYROSINE PHOSPHORYLATION OF MEASLES-VIRUS P-PHOSPHOPROTEIN IN PERSISTENTLY INFECTED NEUROBLASTOMA-CELLS

Replication and encapsidation of measles virus (MV) requires the inter action between the nuclear protein (N) and the phosphoprotein (P). It is known that both proteins are phosphorylated on serine and threonine residues. Recently we have shown that N is phosphorylated on tyrosine in persistently-infected mouse neuroblastoma cells (NS20Y/MS). Here, we show that P in NS20Y/MS is also phosphorylated on tyrosine. To inve stigate whether cellular tyrosine kinases can bind and phosphorylate P , a solid phase kinase assay was employed. We show that bacterially-ex pressed MV P fragments, were phosphorylated on tyrosine by purified mo use c-Src protein-tyrosine kinase and when mixed with uninfected neuro blastoma cell (NS20Y) extracts, these P fragments were phosphorylated on tyrosine in addition to serine and threonine. These results imply t hat MV P is a substrate for tyrosine phosphorylation by cellular tyros ine kinase(s).