Characterization of tumour virus proteins. I. Radioimmunoassay of the P27 protein of avian viruses.

The major structural protein of avian oncornaviruses, a core component of about 27000 daltons, has been measured by radioimmunoassay. The purified protein was labelled with 125Iodine by chloramine-T method. The immune serum titer was defined as the highest serum dilution able to precipitate 50% of the labelled antigen present in the system. Standard competition curve was constructed in order to determine the equivalents of protein, in a system with limiting antibody concentration. In the experimental conditions used, 0.14 ng of AMV-P27 inhibited 50% of 125I-AMV-P27 (1.0 ng) precipitation. The 125I-AMV-P27 vs anti-AMV-P27 system was used to study the competition of normal cells, purified virus suspension, productive cells and supernatant fluids. Most of the chicken embryo fibroblasts showed expression of this viral component. The phenomena of cell transformation, the increase in total protein, and the expression of P27 were studied in rapid transformation of CEF by RSV-SRA.