This is a solo version of the zf-CXXC domain with a conserved CXXCXXCX(n)C, zinc-binding motif. This is, thus far, only detected in the plant lineage in diverse chromatin proteins [1]. Structural comparisons show that the mono-CXXC is homologous to the structural- zinc binding domain of medium chain dehydrogenases [1]. The regular zf-CXXC domain binds nonmethyl-CpG dinucleotides.

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