Involved in transcriptional silencing and telomere length regulation. Its role in telomere length regulation results from either a block in elongation or promoting degradation of the telomere ends. Loss of RIF1 function results in derepression of an HMR silencer, whose ARS consensus element has been deleted, and in the elongation of telomeres. RAP1 may target the binding of RIF1 to silencers and telomeres. Interacts with RIF1 and RAP1 C-terminus. Present with 589 molecules/cell in log phase SD medium.