<p>The FCH domain is a short conserved region of around 60 amino acids first described as a region of homology between FER and CIP4 proteins [<cite idref="PUB00001037"/>]. Many proteins containing an FCH domain are involved in the regulation of cytoskeletal rearrangements, vesicular transport and endocytosis. In the CIP4 protein the FCH domain binds to microtubules [<cite idref="PUB00018146"/>]. The FCH domain is always found N-terminally and is followed by a coiled-coil region.</p><p>Proteins containing an FCH domain can be divided in 3 classes [<cite idref="PUB00018147"/>]:<ol><li>A subfamily of protein kinases usually associated with an SH2 domain:<ul><li>Fps/fes (Fujimani poultry sarcoma/feline sarcoma) proto-oncogenes. They are non-receptor protein-tyrosine kinases preferentially expressed in myeloid lineage. The viral oncogene has an unregulated kinase activity which abrogates the need for cytokines and influences differentiation of haematopoietic progenitor cells.</li><li>Fes related protein (fer). It is an ubiquitously expressed homologue of Fes.</li></ul></li><li>Adaptor proteins usually associated with a C-terminal SH3 domain:<ul><li>Schizosaccharomyces pombe CDC15 protein. It mediates cytoskeletal rearrangements required for cytokinesis. It is essential for viability.</li><li>CD2 cytoplasmic domain binding protein.</li><li>Mammalian Cdc42-interacting protein 4 (CIP4). It may act as a link between Cdc42 signaling and regulation of the actin cytoskeleton.</li><li>Mammalian PACSIN proteins. A family of cytoplasmic phosphoproteins playing a role in vesicle formation and transport.</li></ul></li><li>A subfamily of Rho-GAP proteins:<ul><li> Mammalian RhoGAP4 proteins. They may down-regulate Rho-like GTPases in hematopoietic cells.</li><li>Yeast hypothetical protein YBR260C.</li><li>Caenorhabditis elegans hypothetical protein ZK669.1.</li></ul></li></ol></p>