Analysis of Marek's disease virus serotype 1-specific phosphorylated polypeptides in virus-infected cells and Marek's disease lymphoblastoid cells.

By use of monoclonal antibodies, a virus-specific cytoplasmic antigen related to phosphorylated polypeptides specific to serotype 1 of Marek's disease virus (MDV)-related viruses (MDV1) has been identified in all MD tumour cell lines examined, as well as in infected cells and in tumour lesions of chickens with MD. At least two phosphorylated polypeptides with mol. wt. 39,000 (39K) to 36K and 24K (pp39/36 and pp24, respectively) were identified in the MD tumour cell line H10 cultured at 33 degrees C by immunoprecipitation with monoclonal antibody M21 which reacts with virus-specific phosphorylated polypeptides. These polypeptides were not detected in cells infected with MDV-related viruses of serotype 2 or 3. Immunoblot analysis indicated that these two polypeptides contained a serotype 1-specific epitope recognized with M21. An additional 41K polypeptide appeared in different virus strains of serotype 1. These polypeptides were found to contain phosphorylated serine but no detectable phosphorylated tyrosine or phosphorylated threonine. Cell fractionation indicated that the two phosphorylated polypeptides were mainly associated with smooth and rough endoplasmic reticulum fractions of cells infected with MDV1. Furthermore, the mRNA coding for pp39/36 could be separated from that coding for pp24 on a sucrose density gradient. These results suggest that pp24 and pp39/36 are translated from distinct mRNAs and encoded from overlapping genes or separate regions with partial DNA homology in the MDV1 genome.