FYN protein, also known as p59-FYN, SLK, or SYN, is a 59 kDa protein composed of 537 amino acids, encoded by the FYN gene located on chromosome 6q21. It is a member of the Src family of non-receptor tyrosine kinases and is primarily localized to the cytoplasmic leaflet of the plasma membrane. FYN plays crucial roles in various biological processes, including cell growth, survival, adhesion, cytoskeletal remodeling, and immune response. In the nervous system, it is involved in synaptic transmission, axon guidance, and neuronal differentiation. FYN also participates in T-cell receptor signaling pathways, regulating T-cell differentiation and proliferation. Additionally, it has been implicated in cancer progression due to its involvement in cell cycle regulation and its potential as a proto-oncogene.