Component of the shelterin complex (telosome) that is involved in the regulation of telomere length and protection. Shelterin associates with arrays of double-stranded TTAGGG repeats added by telomerase and protects chromosome ends; without its protective activity, telomeres are no longer hidden from the DNA damage surveillance and chromosome ends are inappropriately processed by DNA repair pathways. Plays a role in shelterin complex assembly (By similarity). Monomer. Found in a complex with POT1; TERF1 and TNKS1. Component of the shelterin complex (telosome) composed of TERF1, TERF2, TINF2, TERF2IP, ACD and POT1 (By similarity). Interacts with TERF1. The TBM domain mediates interaction with TERF1.