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ADDz domain found in ATRX (alpha-thalassemia/mental retardation, X-linked) ADDz_ATRX is a PHD-like zinc finger domain of ATRX, which belongs to the SNF2 family of chromatin remodeling proteins. ATRX is a large chromatin-associated nuclear protein with two domains, ADDz_ATRX at the N-terminus, followed by a C-terminal ATPase/helicase domain. The ADDz_ATRX domain recognizes a specific methylated histone, and this interaction is required for heterochromatin localization of the ATRX protein. Missense mutations in either of the two ATRX domains lead to the X-linked alpha-thalassemia and mental retardation syndrome; however the mutations in the ADDz_ATRX domain produce a more severe disease phenotype that may also relate to disturbing unknown functions or interaction sites of this domain. The ADDz domain is also present in chromatin-associated proteins cytosine-5-methyltransferase 3 (Dnmt3); it is a PHD-like zinc finger motif that contains two parts, a C2-C2 and a PHD-like zinc finger. PHD zinc finger domains have been identified in more than 40 proteins that are mainly involved in chromatin mediated transcriptional control; the classical PHD zinc finger has a C4-H-C3 motif that spans about 50-80 amino acids. In ADDz, the conserved histidine residue of the PHD finger is replaced by a cysteine, and an additional zinc finger C2-C2 like motif is located about twenty residues upstream of the C4-C-C3 motif.
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