p59-Fyn is a member of the protein-tyrosine kinase oncogene family. p59fyn is a membrane-associated non-receptor protein tyrosine kinase that belongs to the Src-family of kinases. p59-Fyn encodes a membrane-associated tyrosine kinase which is implicated in the control of cell growth. p59-Fyn associates with the p85 subunit of phosphatidylinositol 3-kinase and interacts with the fyn-binding protein. The unique N-terminal domain of p59fyn interacts with the CD3 and eta chains of the TcR. p59fyn can bind other proteins (p82 and p116) throµgh its SH2 and SH3 domains, which may act as substrates or regulators of fyn activity. p59fyn is highly expressed in brain sµggesting that it may have a role in the sensory nervous network and in myelination at early stages of CNS formation. Distinct isoforms exist due to alternative splicing.