A non-receptor protein tyrosine kinase that is localized to focal adhesions and is a central component of integrin-mediated signal transduction PATHWAYS. focal adhesion kinase 1 interacts with paxillin and undergoes phosphorylation in response to adhesion of cell surface integrins to the extracellular matrix. Phosphorylated p125FAK protein binds to a variety of SH2 DOMAIN and SH3 DOMAIN containing proteins and helps regulate cell adhesion and CELL MIGRATION.