Protein tyrosine kinases belonging to the src family.

There are nine non-receptor-type protein tyrosine kinases that show a high level of similarity in their primary structures and in the structures of their functional domains. Together, they are called the src family. They seem to have common sites specific for oncogenic activation. Recent findings suggest that the kinases are closely associated with cell surface molecules and that they mediate extracellular signals through the activation of their tyrosine kinase activity. They appear to act more on the differentiated phenotype than in haemopoietic cell proliferation. Possible functions of the products of the lck, fyn, lyn and fgr genes in lymphocytes and monocytes are discussed.