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SET (Su(var)3-9, Enhancer-of-zeste, Trithorax) domain superfamily The Su(var)3-9, Enhancer-of-zeste, Trithorax (SET) domain superfamily corresponds to SET domain-containing lysine methyltransferases, which catalyze site and state-specific methylation of lysine residues in histones that are fundamental in epigenetic regulation of gene activation and silencing in eukaryotic organisms. SET domains appear to be protein-protein interaction domains. It has been demonstrated that SET domains mediate interactions with a family of proteins that display similarity with dual-specificity phosphatases (dsPTPases). A subset of SET domains has been called PR domains. These domains are divergent in sequence from other SET domains, but also appear to mediate protein-protein interaction. The SET domain consists of two regions known as N-SET and C-SET. C-SET forms an unusual and conserved knot-like structure of probable functional importance. In addition to N-SET and C-SET, an insert region (I-SET) and flanking regions of high structural variability form part of the overall structure. Some family members contain a pre-SET domain, which is found in a number of histone methyltransferases (HMTase), and a post-SET domain, which harbors a zinc-binding site.
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