MADS-box

The MADS box is a conserved sequence motif. The genes which contain this motif are called the MADS-box gene family. The MADS box encodes the DNA-binding MADS domain. The MADS domain binds to DNA sequences of high similarity to the motif CC[A/T]₆GG termed the CArG-box. MADS-domain proteins are generally transcription factors. The length of the MADS-box reported by various researchers varies somewhat, but typical lengths are in the range of 168 to 180 base pairs, i.e. the encoded MADS domain has a length of 56 to 60 amino acids. There is evidence that the MADS domain evolved from a sequence stretch of a type II topoisomerase in a common ancestor of all extant eukaryotes.

The first MADS-box gene to be identified was ARG80 from budding yeast, Saccharomyces cerevisiae, but was at that time not recognized as a member of a large gene family. The MADS-box gene family got its name later as an acronym referring to the four founding members, ignoring ARG80:

MADS-box genes were detected in nearly all eukaryotes studied. While the genomes of animals and fungi generally possess only around one to five MADS-box genes, genomes of flowering plants have around 100 MADS-box genes. Two types of MADS-domain proteins are distinguished; the SRF-like or Type I MADS-domain proteins and the MEF2-like (after MYOCYTE-ENHANCER-FACTOR2) or Type II MADS-domain proteins. SRF-like MADS-domain proteins in animals and fungi have a second conserved domain, the SAM (SRF, ARG80, MCM1) domain. MEF2-like MADS-domain proteins in animals and fungi have the MEF2 domain as a second conserved domain. In plants, the MEF2-like MADS-domain proteins are also termed MIKC-type proteins referring to their conserved domain structure, where the MADS (M) domain is followed by an Intervening (I), a Keratin-like (K) and a C-terminal domain. In plants, MADS-domain protein form tetramers and this is thought to be central for their function. The structure of the tetramerisation domain of the MADS-domain protein SEPALLATA3 was solved illustrating the structural basis for tetramer formation

A geneticist intensely investigating MADS-box genes is Günter Theißen at the University of Jena. For example, he and his coworkers could show by these genes that the order of Gnetales is related more closely to the conifers than with the flowering plants.

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