Characterization and functional allotment of proto-oncogenes belonging to the src family.

Eight proto-oncogenes encode cytoplasmic protein tyrosine kinases whose primary structures are closely related to that of p60proto-src. This group of related genes is called the src-family. Their products share common structures: namely, a glycine residue at position 2 from the N terminus, a unique domain, a modulatory domain (SH2, SH3), a kinase (catalytic) domain, and a regulatory domain. Oncogenic activation of these genes may occur by various mutations such as 1) deletion or substitution of the tyrosine at the C-terminal position, 2) mutation at a defined position in the kinase domain or 3) deletion or mutation in the modulatory domain. The expressions of the proto-oncogenes of this family are tissue specific and are unique for each gene, suggesting functional allotment of these gene products. In the hematopoietic system, the genes appear to be expressed in specific cell lineages. In this paper, the functional allotments of these genes in the hematopoietic system are considered with special reference to the functions of lck, lyn, and fyn in cells of T and B lymphocyte lineages.