Fgr is a member of the Src tyrosine kinase family. It has a membrane-associated amino-terminal domain that is highly divergent from other family members, internal conserved SH2 and SH3 domains and a highly conserved carboxy-terminal tyrosine kinase catalytic domain. Tyrosine 412 is located in the activation loop, and phosphorylation of this residue is critical for the activation of Fgr tyrosine kinase activity. c-Fgr is predominantly expressed in cells of hematopoietic origin including differentiated myeloid cells, NK and B cells. Fgr plays an important role in the signaling cascade from membrane receptors lacking intrinsic tyrosine kinase activity such as Bcr, FcR, and the integrin family of receptors. It was demonstrated that Fgr functions as a selective inhibitor of beta2 integrin-mediated signaling and Syk kinase function in monocytes.