Highly conserved protein domains of approximately 130 to 140 amino acids. The SET domain was first identified in the Drosophila proteins (S)u(var)3-9, (E)nhancer-of-zeste and (T)rithorax and occurs in other proteins with a variety of functions, including histone-lysine N-methyltransferases. Structurally, it consists of BETA-SHEETS interspersed among loops and turns that result in an "L" shape. The most conserved motifs are a stretch at the C-terminal that contains a strictly conserved tyrosine residue and an adjacent loop that the C-terminal segment passes through to form a "knot". These motifs and especially the tyrosine residue are essential for S-ADENOSYLMETHIONINE binding and catalysis. The PR domain has high homology to the catalytic region of the SET domain and occurs at the N-terminal of PRDM proteins such as PRDM1 PROTEIN.
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