The MADS‐box family of transcription factors has been defined on the basis of primary sequence similarity amongst numerous proteins from a diverse range of eukaryotic organisms including yeasts, plants, insects, amphibians and mammals. The MADS‐box is a conserved motif found within the DNA‐binding domains of these proteins and the name refers to four of the originally identified members: MCM1, AG, DEFA and SRF. Several proteins within this family have significant biological roles. For example, the human serum‐response factor (SRF) is involved in co‐ordinating transcription of the proto‐oncogene c‐fos, whilst MCM1 is central to the transcriptional control of cell‐type specific genes and the pheromone response in the yeast Saccharomyces cerevisiae. The RSRF/MEF2 proteins comprise a subfamily of this class of transcription factors which are key components in muscle‐specific gene regulation. Moreover, in plants, MADS‐box proteins such as AG, DEFA and GLO play fundamental roles during flower development.

The MADS‐box is a contiguous conserved sequence of 56 amino acids, of which 9 are identical in all family members described so far. Several members have been shown to form dimers and consequently two functional regions within the MADS‐box have been defined. The N‐terminal half is the major determinant of DNA‐binding specificity whilst the C‐terminal half is necessary for dimerisation. This organisation allows the potential formation of numerous proteins, with subtly different DNA‐binding specificities, from a limited number of genes by heterodimerisation between different MADS‐box proteins. The majority of MADS‐box proteins bind similar sites based on the consensus sequence CC(A/T)₆ GG although each protein apparently possesses a distinct binding specificity. Moreover, several MADS‐box proteins specifically recruit other transcription factors into multi‐component regulatory complexes. Such interactions with other proteins appears to be a common theme within this family and play a pivotal role in the regulation of target genes.