Results from an in vitro kinase assay. Proteins were extracted from cryostat tissue sections, immunoprecipitated with anti-ALK, and incubated with radioactive kinase substrate. The samples were then resolved using sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography. Phosphorylated proteins of 97 kD and 104 kD were detected in tumor tissue from patients S.N. and D.F., respectively. 80-kD phosphorylated NPM-ALK was present in the t(2;5)⁺ cell line SU-DHL-1. No ALK proteins were present in the tonsil lysates used as negative controls.