Figure 1. Capping activities at S. cerevisiae and human telomeres. In S. cerevisiae, Rap1 and Rif2 inhibit 5′-3′ resection of the telomeric DNA ends and also repress the NHEJ repair pathway. Rif1 supports the function of the CST complex in preventing excessive resection at telomeric ends and Mec1-dependent checkpoint activation. In humans, TRF2 represses ATM signaling and the NHEJ pathway, whereas POT1 prevents ATR activation by inhibiting the binding of the ssDNA-binding protein RPA. POT1 and RAP1 block HR. ATM, ataxia telangiectasia mutated; ATR, ataxia telangiectasia and Rad3-related protein; CST, Cdc13, Stn1, and Ten1; HR, homologous recombination; NHEJ, non-homologous end joining; RPA, replication protein A.