The chromatin organization modifier (chromodomain) is a protein domain of 40-50 amino acids involved in chromatin remodeling and regulation of gene expression in eukaryotes (Koonin, Zhou and Lucchesi 1995; Cavalli and Paro 1998). Examples of chromodomains are for instance, the Drosophila melanogaster Heterochromatin Protein 1 (HP1), the Histone acetyltransferase MOF, the protein Polycomb (PC), and the Suppressor of variegation (Suvar).
Chromodomains have been identified in a variety of proteins that play a role in chromatin modification, including factors that activate and repress transcription. Several studies have demonstrated that chromodomains are responsible for chromatin targeting and for interactions between different proteins as a stand-alone protein interaction module (Cowell and Austin 1997; Strutt and Paro 1997; Lachner et al. 2001, as a RNA-binding module (Akhtar et al. 2000), and most recently, as a DNA-binding module (Bouazoune et al. 2002). Accounting that the chromodomain confers binding specificity to chromatin, these functions may in fact be interdependent (Kelley et al. 1999). Also, a second chromodomain motif termed chromoshadow domain has been described at the C-terminal end of several chromodomain-containing proteins such as HP1 (Aasland and Stewart 1995).