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Hox genes (also known as homeotic genes) are a group of related genes that control the body plan of an embryo along the anterior-posterior (head-tail) axis. After the embryonic segments have formed, the Hox proteins determine the type of segment structures (e.g. legs, antennae, and wings in fruit flies or the different types of vertebrae in humans) that will form on a given segment. Hox proteins thus confer segmental identity, but do not form the actual segments themselves. Hox genes are defined as having the following properties: * Their protein product is a transcription factor * They contain a DNA sequence known as the homeobox * In many animals, the organization of the Hox genes in the chromosome is the same as the order of their expression along the anterior-posterior axis of the developing animal, and are thus said to display colinearity. == Hox genes code for transcription factors == The products of Hox genes are Hox proteins. Hox proteins are transcription factors, which are proteins that are capable of binding to specific nucleotide sequences on the DNA called enhancers where they either activate or repress genes. The same Hox protein can act as a repressor at one gene and an activator at another. The ability of Hox proteins to bind DNA is conferred by a part of the protein referred to as the homeodomain. The homeodomain is a 60-amino-acid-long DNA-binding domain (encoded by its corresponding 180-base-pair DNA sequence, the homeobox). This amino acid sequence folds into a "helix-turn-helix" (i.e. homeodomain fold) motif that is stabilized by a third helix. The consensus polypeptide chain is (typical intron position noted with dashes):〔http://www.csb.ki.se/groups/tbu/homeo/consensus.gif〕 RRRKRTA-YTRYQLLE-LEKEFLF-NRYLTRRRRIELAHSL-NLTERHIKIWFQN-RRMK-WKKEN 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hox gene」の詳細全文を読む スポンサード リンク
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