Structural and functional motifs of the Rous sarcoma virus src protein.

Site-directed mutagenesis techniques have been utilized to define important structural and functional domains within the RSV src gene product, pp60src. Deletion mutations within the amino terminal one-half of the src gene which impinge upon a region of the src protein delineated by amino acid residues 143 to 169 yielded transformation defective viruses. Src proteins encoded by such RSV mutants exhibited diminished tyrosine protein kinase activity in vitro and only slightly reduced levels of in vivo tyrosine protein kinase activity. We speculate that these structurally altered proteins are defective for target protein recognition. Point mutations and linker insertion mutations within the putative catalytic domain of pp60src served to block the transforming activity of mutant viruses. Mutant viruses encode src proteins that exhibited substantially reduced levels of tyrosine protein kinase activity both in vitro and in vivo.