Focal adhesion kinase was initially identified as a major 125 kDa substrate for the intrinsic protein tyrosine kinase activity of Src-encoded pp60. The deduced amino acid sequence of FAK p125 has shown it to be a cytoplasmic protein tyrosine kinase whose sequence and structural organization are unique as compared to other proteins described to date. Localization of p125 by immunofluorescence suggests that it is primarily found in cellular focal adhesions leading to its designation as focal adhesion kinase (FAK). FAK is concentrated at the basal edge of only basal keratinocytes that are actively migrating and rapidly proliferating in repairing burn wounds, and is activated and localized to the focal adhesions of spreading keratinocytes in culture.