This is the first TUDOR domain found in SETDB1 enzymes (EC:2.1.1.43) in homosapiens, also known as Eggless in Drosophila [1]. In Drosophila, SetdB1 (Egg) is important for oogenesis and the silencing of chromosome 4 [2]. SET domain, bifurcated 1 (SETDB1) is a histone methyltransferase (HMT) that methylates lysine 9 on histone H3 (H3K9). The enzymatic activity of SETDB1, in association with MBD1-containing chromatin-associated factor 1 (MCAF1), converts H3K9me2 to H3K9me3 and represses subsequent transcription. SETDB1 is amplified in cancers such as melanoma and lung cancer, and increased expression of SETDB1 promotes tumorigenesis in a zebrafish melanoma model. In addition, SETDB1 is required for endogenous retrovirus silencing during early embryogenesis, inhibition of adipocyte differentiation, and differentiation of mesenchymal cells into osteoblasts [1]. The tandem Tudor domains in the N-terminal region are involved in protein-protein interactions [2]. The second tudor domain is Pfam:PF18385.

1: Analysis of the subcellular localization of the human histone methyltransferase SETDB1. Tachibana K, Gotoh E, Kawamata N, Ishimoto K, Uchihara Y, Iwanari H, Sugiyama A, Kawamura T, Mochizuki Y, Tanaka T, Sakai J, Hamakubo T, Kodama T, Doi T; Biochem Biophys Res Commun. 2015;465:725-731. PMID:26296461

2: Ubiquitination of Lysine 867 of the Human SETDB1 Protein Upregulates Its Histone H3 Lysine 9 (H3K9) Methyltransferase Activity. Ishimoto K, Kawamata N, Uchihara Y, Okubo M, Fujimoto R, Gotoh E, Kakinouchi K, Mizohata E, Hino N, Okada Y, Mochizuki Y, Tanaka T, Hamakubo T, Sakai J, Kodama T, Inoue T, Tachibana K, Doi T; PLoS One. 2016;11:e0165766. PMID:27798683