Figure 2.

Discovery of tyrosine phosphorylation. Middle T antigen was immunoprecipitated from polyomavirus-infected cells, and immunoprecipitates were labelled by incubation with ³²P. Middle T antigen was purified, and the products of partial acid hydrolysis were separated by electrophoresis (a) or on two dimensions by electrophoresis and chromatography (b). Phosphorylated amino acids were detected by autoradiography and identified by reference to standards indicated by dotted circles. P.THR, phospho-threonine; P.TYR, phospho-tyrosine; P.SER, phospho-serine. Reproduced from Eckhart et al. [53] with permission.