Negatively regulates telomere length. Appears to play no role in transcriptional silencing of telomeric loci. Recruited to telomeres by interaction with taz1. Does not interact with rap1, unlike the orthologous protein of budding yeast. Localized to telomeres. This interaction may be increased by perturbation of telomere structure, for instance by loss of the rap1 protein. Belongs to the RIF1 family.