MADS-domain transcription factors are ubiquitously present in all plant and animals. In plant MADS-box genes are regulators of floral organ identity. It has a ~60 amino acid DNA-binding domains, and the protein is named after the first four describe members MADS domain (for MCM1, AG, DEF and SRF) and is present in all MADS-domain transcription factor. Structural analysis of animal and yeast MADS domains showed that the N-terminal and central parts of the MADS domain make contacts with the DNA, while the C-terminal part of this domain contributes mainly to protein dimerization, resulting in a DNA-binding protein dimer consisting of two interacting MADS monomers. The MADS-box gene family can be divided into two lineages, type I and type II, based on their protein domain structure. Genes from the type I have only the ~180 bp DNA sequence encoding the MADS domain. The type II lineage contains the well-studied floral homeotic genes. Plant type II MADS-domain proteins have a modular domain structure, which is referred to as the MIKC structure. They contain an N-terminally located DNA-binding MADS domain, followed by the I (intervening) and K (keratinlike) regions, which are essential for dimerization and higher-order complex formation, and finally a highly variable C-terminal domain, which may have roles in protein complex formation and transcriptional regulation.
1. C. Smaczniak, R. G. Immink, G. C. Angenent, K. Kaufmann, Developmental and evolutionary diversity of plant MADS-domain factors: insights from recent studies. Development 139, 3081 (2012).