The fork head protein of <taxon tax_id="7227">Drosophila melanogaster</taxon>, a transcription factor that promotes terminal rather than segmental development, contains neither homeodomains nor zinc-fingers characteristic of other transcription factors [<cite idref="PUB00000827"/>]. Instead, it contains a distinct type of DNA-binding region, containing around 100 amino acids, which has since been identified in a number of transcription factors (including D. melanogaster FD1-5, mammalian HNF-3, human HTLF, <taxon tax_id="4932">Saccharomyces cerevisiae</taxon> HCM1, etc.). This is referred to as the fork head domain but is also known as a 'winged helix' [<cite idref="PUB00000827"/>, <cite idref="PUB00004151"/>, <cite idref="PUB00004800"/>].The fork head domain binds B-DNA as a monomer [<cite idref="PUB00004151"/>], but shows no similarity to previously identified DNA-binding motifs. Although the domain is found in several different transcription factors, a common function is their involvement in early developmental decisions of cell fates during embryogenesis [<cite idref="PUB00004800"/>]. Transcription factor, fork head