Inhibition of the tyrosine kinase activity of v-src, v-fgr, and v-yes gene products by a monoclonal antibody which binds both amino and carboxy peptide fragments of pp60v-src.

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A monoclonal antibody, R2D2, raised to the src gene product of Rous sarcoma virus was found to inhibit the tyrosine protein kinase activity of pp60v-src in autophosphorylation reactions and in reactions involving exogenously added substrates, such as casein and histone. R2D2 also inhibited the enzymatic activity of two related viral transforming proteins, pp70gag-fgr and pp90gag-yes. The inhibitory ability of R2D2 was dependent upon immunoglobulin concentration and could be demonstrated in both immune complexes formed directly with R2D2 and preformed immune complexes to which R2D2 was added. Binding sites in both the amino-terminal 110 amino acid residues and the carboxy-terminal 240 amino acids of pp60v-src were identified for R2D2. These results indicate that at least part of the epitope recognized by R2D2 resides within a region of the src protein which is required for protein kinase activity. The localization of the R2D2 epitope to the amino- as well as to the carboxy-terminal portions of pp60v-src, together with results of studies analyzing the relative binding efficiencies of R2D2 to the intact protein and to V-8 proteolytic fragments of pp60v-src, are consistent with the view that the R2D2 epitope is conformational in nature and that it is assembled from residues contained within both N-terminal and C-terminal regions of the molecule.

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