This domain, approximately 60-70 residues in length, is mainly found in Forkhead box proteins in various Mammalia species [1]. It is a coiled-coil domain, which modulates the dimeric associations of FOXP transcription factors. Several key disease mutations, for instance those found in the IPEX syndrome are located in this domain [2]

1: Foxp4: a novel member of the Foxp subfamily of winged-helix genes co-expressed with Foxp1 and Foxp2 in pulmonary and gut tissues. Lu MM, Li S , Yang H and Morrisey EE; Mech. Dev. 119 SUPPL 1, S197-S202 (2002); PMID:14516685

2: Transcriptional and DNA binding activity Structural and biological features of FOXP3 dimerization relevant to regulatory T cell function is modulated by heterotypic and homotypic protein interactions. Song X, Li B, Xiao Y, Chen C, Wang Q, Liu Y, Berezov A, Xu C, Gao Y, Li Z, Wu SL, Cai Z, Zhang H, Karger BL, Hancock WW, Wells AD, Zhou Z, Greene MI. Cell Rep. 1:665-75 (2012) PMID:22813742