The SNF2-related family of proteins all contain conserved helicase motifs, and have been implicated in transcription regulation, DNA repair, and DNA recombination. The DNA-dependent ATPase activity of these proteins is usually activated by single-stranded, double-stranded, or nucleosomal DNA. The chromodomain helicase DNA binding proteins (CHDs) are a subfamily of the SNF2 family, and includes CHD1, CHD2, CHD3, and CHD4. CHD3 and CHD4 contain N-terminal paired PHD zinc finger motifs (PZF), two heterochromatin binding domains (chromodomains, CDs), and a central SNF2-like helicase/ATPase domain. CHD3 mRNA is widely expressed, and CHD3 protein localizes to the nucleus, but not nucleoli. Both CHD3 and CHD4 were first identified as self-antigens recognized by sera from patients with the autoimmune connective-tissue disease Mi-2 dermatomyositis. In addition, both CHD3 and CHD4 are associated with a nucleosome remodelling and deacetylating (NRD) complex, and facilitate deacetylation of oligonucleosomal histones in vitro. Thus, CHD3 and CHD4 are chromodomain containing proteins that may have important roles in ATP-dependent nucleosome remodelling.