Structure-Function Relationships in Cellular and Viral fps/fes Cytoplasmic Protein-Tyrosine Kinases

A majority of retroviral oncogenes encode protein-tyrosine kinases (PTKs). Both oncogenic PTKs and their normal counterparts can be divided into two classes: receptor-like polypeptides that possess an extracellular region linked by a transmembrane segment to an internal catalytic domain, and cytoplasmic PTKs that are entirely confined to the inside of the cell (see fig. 1). Cytoplasmic PTKs are usually found in association with the plasma membrane and cytoskeleton (Rohrschneider and Gentry, 1984). The cytoplasmic PTKs can be further subdivided into 3 families corresponding to a group of proteins of approximately 60 kDa for which p6Osrc is the prototype, fps/fes gene products, and abl proteins respectively (Hunter and Cooper, 1985).