The role of protein phosphorylation in growth control and oncogenesis is well established.
Both protein-tyrosine kinases (PTKs) and protein-serine kinases (PSKs) act as signal
transducers for growth-factor and cytokine receptors, and activated forms of both types of
protein kinase can act as oncoproteins. In every process that is regulated by
phosphorylation, protein phosphatases play an obligatory role in counteracting the
consequences of protein kinase action. At the time that the first PTK oncogene was …