Chromosomal mapping of murine c-fes and c-src genes.

The murine homologs of two viral oncogenes associated with tyrosine-specific kinase activity have been assigned to different loci in the mouse genome. The segregation of restriction site polymorphisms, as detected by probes that are specific for endogenous c-fes and c-src sequences, was followed in the DNA of recombinant inbred strains. The c-fes gene was mapped to the proximal portion of chromosome 7, very close to the Gpi-1 locus, whereas c-src was linked to the Psp locus on the distal half of chromosome 2.

Chromosomal mapping of murine c-fes and c-src genes

The murine homologs of two viral oncogenes associated with tyrosine-specific kinase activity have been assigned to different loci in the mouse genome. The segregation of restriction site polymorphisms, as detected by probes that are specific for endogenous c-fes and c-src sequences, was followed in the DNA of recombinant inbred strains. The c-fes gene was mapped to the proximal portion of chromosome 7, very close to the Gpi-1 locus, whereas c-src was linked to the Psp locus on the distal half of chromosome 2.

Two different protein kinase activities are associated with the insulin receptor

In intact rat hepatocytes insulin stimulates the phosphorylation of the beta-subunit of its receptor exclusively on serine residues, which are also phosphorylated in the absence of insulin. In contrast, in partially purified insulin receptors derived from these same cells and in highly purified insulin receptors obtained by immunoprecipitation with anti-receptor antibodies, the receptor beta-subunit is phosphorylated solely on tyrosine residues. For both cell-free systems, insulin's stimulatory action on receptor phosphorylation leads to an increase in phosphotyrosine. When partially purified receptors were used to phosphorylate two exogenous substrates, casein and histone, insulin was found to stimulate the phosphorylation of both tyrosine and serine. However, the basal and insulin-stimulated kinase activity of immunoprecipitated receptors was only tyrosine-specific. From these observations we propose that the insulin-receptor complex consists of two different insulin-stimulatable kinase activities: (1) a tyrosine-specific kinase, which is a constituent of the insulin-receptor structure and whose activation is likely to be the first post-binding event in insulin action; and (2) a serine-specific kinase, which is closely associated with the receptor in the cell membrane.