Required for the maintenance of meristems and stem cells through the reduction of DNA damage (PubMed:21781195). Promotes telomere integrity by maintaining telomere length and proper architecture of the chromosome terminus (PubMed:23572541). Negatively regulates telomerase repeat addition processivity (PubMed:23572541). Hampers contacts between enzymatically active telomerase and CST complex (PubMed:25329641). Component of the CST complex, composed of CTC1, TEN1 and STN1. Interacts with STN1 (PubMed:23572541, PubMed:25329641). No interaction with POT1A, but competes with it for STN1 binding (PubMed:25329641). Associates transiently with telomeres. Ubiquitous (PubMed:21781195, PubMed:23572541). High expression in meristematic tissues and in vasculature (PubMed:21781195). Belongs to the TEN1 family.