Immunoprecipitation of protein kinase activity from adenovirus 5-infected cells using antiserum directed against tumour antigens

THE function of transformation proteins coded for by RNA-and DNA-containing tumour viruses is a major question in oncology. A large number of diverse alterations are produced in cells following viral transformation, and such changes are thought to be the result of the action of one or a very few viral gene products. Until recently, very little was known concerning the mechanism of action of such transforming proteins. However, studies carried out by Collett and Erikson with the RNA tumour virus Rous sarcoma virus (RSV) suggested that the RSV transforming protein, src, either possesses or is associated with protein kinase activity1. Using antiserum directed against virus-coded proteins, it was found that phosphorylation of the heavy chain of the antibody occurred when immunoprecipitates containing src protein were incubated with [γ-32P]ATP. No such protein kinase activity was observed in immunoprecipitates using uninfected cell extracts, extracts from cells infected with transformation-defective virus, or control nonimmune serum. These data suggest that alterations in protein phosphorylation may regulate RSV transformation. This concept is quite appealing, as protein phosphorylation is already known to have an important regulatory role in several cellular processes2–4. We show here that antiserum directed against tumour antigens of a DNA virus, human adenovirus type 5 (Ad 5), will also immunoprecipitate protein kinase activity. Further, immunoprecipitates from cells infected with transformation-defective host range mutants of Ad 5 contain reduced levels of protein kinase activity.