homeobox

(= homoeobox)

Conserved DNA sequence originally detected by DNA-DNA hybridization in many of the genes that give rise to homeotic mutants and segmentation mutants in Drosophila. The homeobox consists of about 180 nucleotides coding for a sequence of 60 amino acids in a protein, sometimes termed the homeodomain, of which about 80-90% are identical in the various homeodomains identified from Drosophila. Homeoboxes have also been detected in the genomes of vertebrates, with about 75% amino acid homology and a similar sequence has been found in the MAT gene of yeast. The homeobox codes for a protein domain that is involved in binding to DNA. Three subfamilies of homeobox-containing proteins can be identified, based on the archetypal Drosophila genes engrailed, antennapedia and paired. Interestingly, linear order within genome maps to order of expression in embryo. This may be required for the transcriptional silencing of certain homeotic genes (see Polycomb).