<p>Proteins that regulate developmental gene expression are nuclear proteins [<cite idref="PUB00001890"/>] that containa conserved domain known as the homeobox, the flanking sequences of which differ considerably amongdifferent proteins. The homeodomain includes the helix-turn-helix (HTH) motif which binds to DNA[<cite idref="PUB00004373"/>]. Most proteins which contain a homeobox domain can be classified [<cite idref="PUB00000591"/>, <cite idref="PUB00005101"/>],on the basis of their sequence characteristics, into three subfamilies, engrailed, antennapedia andpaired. The engrailed subfamily plays an important role in Drosophila segmentation and neurogenesis,affecting genes in posterior compartments of the developing embryo. It is also required for thedevelopment of the central nervous system. Homologues found in other species may play a role inneurogenesis, possibly in both the compartmentalisation of the developing neural tube and specificationof particular neuronal populations. Other members of the engrailed subfamily include Drosophila invectedprotein (inv); <taxon tax_id="7460">Apis mellifera</taxon> (Honeybee) E30 and E60; <taxon tax_id="7009">Schistocerca americana</taxon> (American grasshopper) G-En; mammalian and birds En-1 and En-2; <taxon tax_id="7955">Danio rerio</taxon> (Zebrafish) (Brachydanio rerio) Eng-1, -2 and -3; <taxon tax_id="6413">Helobdella triserialis</taxon> (Leech) Ht-En; and <taxon tax_id="6239">Caenorhabditis elegans</taxon> ceh-16.</p> Homeobox engrailed