MeCP2 is a transcription factor that recognizes and binds symmetrically methylated CpG dinucleotides to repress transcription. MeCP2 can associate with the Sin3a/histone deacetylase co-repressor complex and mediate repression in a histone deacetylase dependent manner. In extracts from rodent tissues, cultured cells and Xenopus laevis oocytes, we find that only a small amount of mammalian MeCP2 interacts with Sin3a and that this interaction is not stable. Purification of rat brain MeCP2 (MW 53 kDa) indicates no associated proteins despite an apparent molecular weight by size exclusion chromatography of 400-500 kDa. Biophysical analysis demonstrates that the large apparent size is not due to homo-multimerisation, as MeCP2 consistently behaves as a monomeric protein that has an elongated shape. Our findings indicate the MeCP2 is not an obligate component of the Sin3a co-repressor complex and may therefore engage a more diverse range of co-factors for repressive function.

It's been theorized for a long time that the protein, MeCP2, needs to bind with other molecules in order to do its job of shutting down other genes. These other molecules include Sin3A and HDAC (which has been implicated in cancer). Dr. Adrian Bird, Chairman of the RSRF Scientific Advisory Board, presents data suggesting that in fact, MeCP2 rarely binds with these other molecules. Furthermore, he finds that MeCP2 is very large and has an elongated shape. More research will need to be done to ascertain whether MeCP2 acts alone or whether it binds with many different molecules depending on the situation.