Binds directly to 5'-TTAGGG-3' repeats in telomeric DNA (By similarity). Associates with the telomerase complex at sites of active telomere processing and positively regulates telomere elongation (By similarity). Important for TERT binding to chromatin, indicating a role in recruitment of the telomerase complex to telomeres (PubMed:23685356). Also plays a role in the alternative lengthening of telomeres (ALT) pathway in telomerase-negative cells where it promotes formation and/or maintenance of ALT-associated promyelocytic leukemia bodies (APBs) (By similarity). Enhances formation of telomere C-circles in ALT cells, suggesting a possible role in telomere recombination (By similarity). Might also be involved in the DNA damage response at telomeres (By similarity). Associates with the telomerase holoenzyme complex. Interacts with DKC1, XRCC6 and COIL. Predominantly detected in cytoplasm. Localizes in a dynamic manner to actively processed telomeres. Localizes to the periphery of Cajal bodies. Associates with PML nuclear bodies in telomerase-negative cells. The homeobox domain is required for binding to 5'-TTAGGG-3' repeats in telomeres, and for telomere localization. Reported to have transcriptional repression activity in vitro. However, it is unclear whether this protein has any function in transcription in vivo.