The PWWP domain is named after a conserved Pro-Trp-Trp-Pro motif [1]. The domain binds to Histone-4 methylated at lysine-20, H4K20me, suggesting that it is methyl-lysine recognition motif. Removal of two conserved aromatic residues in a hydrophobic cavity created by this domain within the full-length protein, Pdp1, abolishes the interaction o f the protein with H4K20me3. In fission yeast, Set9 is the sole enzyme that catalyses all three states of H4K20me, and Set9-mediated H4K20me is required for efficient recruitment of checkpoint protein Crb2 to sites of DNA damage. The methylation of H4K20 is involved in a diverse array of cellular processes, such as organising higher-order chromatin, maintaining genome stability, and regulating cell-cycle progression [2].

1: WHSC1, a 90 kb SET domain-containing gene, expressed in early development and homologous to a Drosophila dysmorphy gene maps in the Wolf-Hirschhorn syndrome critical region and is fused to IgH in t(4;14) multiple myeloma. Stec I, Wright TJ, van Ommen GJB, de Boer PAJ, van Haeringen A, Moorman AFM, Altherr MR, den Dunnen JT; Hum Mol Genet 1998;7:1071-1082. PMID:9618163

2: Regulation of Set9-mediated H4K20 methylation by a PWWP domain protein. Wang Y, Reddy B, Thompson J, Wang H, Noma K, Yates JR 3rd, Jia S; Mol Cell. 2009;33:428-437. PMID:19250904

3: The PWWP domain of mammalian DNA methyltransferase Dnmt3b defines a new family of DNA-binding folds. Qiu C, Sawada K, Zhang X, Cheng X; Nat Struct Biol. 2002;9:217-224. PMID:11836534