Functions of Sir2 in yeast. Sir2 mediates silencing at telomeres, along with Sir3, Sir4, and Ku, (A) and at the repeated rDNA (B) without these other factors. Telomeric proteins respond to DNA double-strand breaks (DSBs) by moving to sites of damage in S-phase in a pathway requiring MEC1,RAD9, RAD53. In a sir2 mutant, homologous recombination in the rDNA increases leading to more ERCs.