third malignant brain tumor (MBT) repeat found in the Drosophila melanogaster Polycomb protein Sfmbt (dSfmbt)-like family
The dSfmbt-like family includes Drosophila melanogaster Scm-like with four MBT domain-containing protein 1 (dSfmbt), as well as its two vertebrate homologs, MBT domain-containing protein 1 (MBTD1) and Lethal(3)malignant brain tumor-like protein 2 (L3MBTL2). dSfmbt is a Polycomb group (PcG) repressor involved in epigenetic regulation of gene expression. MBTD1 and L3MBTL2, also called L(3)mbt-like protein 2, are putative PcG proteins that specifically bind to monomethylated and dimethylated 'Lys-20' on histone H4. L3MBTL2 also binds histone H3 peptides which are monomethylated or dimethylated on 'Lys-4', 'Lys-9' or 'Lys-27'. Members of this family contain four MBT (malignant brain tumor) repeats. The MBT repeat is a protein module that recognizes methylated lysine residues on histones. MBT repeats contain a semi-aromatic cage to accommodate methyllysine and show specificity towards the lower methylation states of lysine. This model corresponds to the third MBT repeat that does not seem to contain a semi-aromatic cage and may not bind methylated lysine residues.
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