This domain contains eight conserved cysteine residues that bind to two zinc ions. The CXXC domain is found in a variety of chromatin-associated proteins. This domain binds to nonmethyl-CpG dinucleotides. The domain is characterised by two repeats [3], and shows a peculiar internal duplication in which the second unit is inserted into the first one [4]. Each of these units is characterised by four conserved cysteines, displaying a CXXCXXCX(n)C motif that chelate a Zn+2 ion. The DNA binding interface has been identified by NMR [3]. In eukaryotes, the CXXC domain is found in stramenopiles, plants and metazoans. Plants possess a mono-CXXC domain that is present in distinct chromatin proteins [4]. Structural comparisons show that the mono-CXXC is homologous to the structural-zinc binding domain of medium chain dehydrogenases [4].

1: A component of the transcriptional repressor MeCP1 shares a motif with DNA methyltransferase and HRX proteins. Cross SH, Meehan RR, Nan X, Bird A; Nat Genet 1997;16:256-259. PMID:9207790

2: Activation of mammalian DNA methyltransferase by cleavage of a Zn binding regulatory domain. Bestor TH; EMBO J 1992;11:2611-2617. PMID:1628623

3: Solution structure of the nonmethyl-CpG-binding CXXC domain of the leukaemia-associated MLL histone methyltransferase. Allen MD, Grummitt CG, Hilcenko C, Min SY, Tonkin LM, Johnson CM, Freund SM, Bycroft M, Warren AJ; EMBO J. 2006;25:4503-4512. PMID:16990798

4: Natural history of eukaryotic DNA methylation systems. Iyer LM, Abhiman S, Aravind L; Prog Mol Biol Transl Sci. 2011;101:25-104. PMID:21507349