(3) Telomere repair domains DOT1 (PF08123) is a protein that methylates histones and is needed for yeast's DNA damage checkpoint. It regulates gene expression by methylating histone H3. It methylates histone H79's lysine 79 (Lys-3). It identifties Dot1p as the first disruptor of telomere silencing in yeast, where it is associated with gene silencing and the localization of the silent information regulator (SIR) complex. In higher eukaryotes, methylation by this enzyme can be employed to differentiate chromatin domains.