Homeobox

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Ribbon model of the homeodomain of the Antennapedia protein of the fruit fly ( Drosophila melanogaster ), bound to a DNA fragment, according to PDB 1AHD .

A homeobox is a characteristic sequence of homeotic genes that codes for the homeodomain. The homeodomain is a protein domain (i.e. part of a protein) that can bind to DNA.

Genes that contain a homeobox and are arranged in groups are called Hox genes in vertebrates such as humans , Hom genes in articulated animals such as insects or generally homeotic genes . They make up the Hox gene family. The homeobox genes code for transcription factors that typically switch a whole cascade of other functionally related genes on and off, for example those genes that contribute to the development of a leg. The homeodomain itself binds non-specifically to various DNA sequences. The specificity of the binding to certain DNA sequences is brought about by other parts of the transcription factor. An already well-studied in the impact chain transcription factor is the Bicoid - protein .

Mutations in Hox genes can lead to redundant legs (for example legs instead of antennas in flies - "Antennapedia mutants"). In this way you can give indications of the homology of certain organs. Usually, however, mutations cause such a severe developmental disorder that the affected embryos die.

Hox genes were first discovered in the fruit fly Drosophila melanogaster , and later in many different species, from other insects to reptiles and mammals . Even single-celled yeasts have comparable genes. This suggests that this family of genes appeared very early in the evolution of eukaryotes . This is why the sequences of Hox genes are also often used to determine relationships for systematics .

The most famous gene clusters of Hom genes in Drosophila are:

  • the Antennapedia Complex (ANT-C); he controls the formation of the head and the anterior breast segments; it comprises approximately 100,000 base pairs (100 kbp); ANT-C consists of the gene segments
    • labial
    • proboscidea
    • deformed
    • Sex combs reduced
    • Antennapedia
  • the Bithorax complex (BX-C); it affects the rear segments of the chest and the abdomen. At 300 kBp, this complex is significantly longer than ANT-C; BX-C consists of the gene segments
    • Ultrabithorax
    • Abdominal A
    • Abdominal B

See also

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