Telomerase is a ribonucleoprotein enzyme essential for the replication of chromosome termini in most eukaryotes. Active in progenitor and cancer cells. Inactive, or very low activity, in normal somatic cells. Catalytic component of the teleromerase holoenzyme complex whose main activity is the elongation of telomeres by acting as a reverse transcriptase that adds simple sequence repeats to chromosome ends by copying a template sequence within the RNA component of the enzyme. Catalyzes the RNA-dependent extension of 3'-chromosomal termini with the 6-nucleotide telomeric repeat unit, 5'-TTAGGG-3'. The catalytic cycle involves primer binding, primer extension and release of product once the template boundary has been reached or nascent product translocation followed by further extension. More active on substrates containing 2 or 3 telomeric repeats. Telomerase activity is regulated by a number of factors including telomerase complex-associated proteins, chaperones and polypeptide modifiers. Modulates Wnt signaling. Plays important roles in aging and antiapoptosis (By similarity). a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Catalytic component of the telomerase holoenzyme complex composed of one molecule of TERT, one molecule of WRAP53/TCAB1, two molecules of H/ACA ribonucleoprotein complex subunits DKC1, NOP10, NHP2 and GAR1, and a telomerase RNA template component (TERC). The telomerase holoenzyme complex is associated with TEP1, SMG6/EST1A and POT1. The molecular chaperone HSP90/P23 complex is required for correct assembly and stabilization of the active telomerase. Interacts directly with HSP90A and PTGES3. Interacts with HSPA1A; the interaction occurs in the absence of TERC and dissociates once the complex has formed. Interacts with RAN; the interaction promotes nuclear export of TERT. Interacts with XPO1. Interacts with PTPN11; the interaction retains TERT in the nucleus. Interacts with NCL (via RRM1 and C-terminal RRM4/Arg/Gly-rich domains); the interaction is important for nucleolar localization of TERT (By similarity). Interacts with SMARCA4 (via the bromodomain); the interaction regulates Wnt-mediated signaling (By similarity). Interacts with MCRS1 (isoform MCRS2); the interaction inhibits in vitro telomerase activity (By similarity). Interacts with PIF1; the interaction has no effect on the elongation activity of TERT (By similarity). Interacts with PML; the interaction recruits TERT to PML bodies and inhibits telomerase activity (By similarity). Interacts with GNL3L (By similarity). Interacts with isoform 1 and isoform 2 of NVL (By similarity). Interacts with DHX36 (By similarity). Interacts with ATF7 (By similarity). Shuttling between nuclear and cytoplasm depends on cell cycle, phosphorylation states, transformation and DNA damage. Diffuse localization in the nucleoplasm. Enriched in nucleoli of certain cell types. Translocated to the cytoplasm via nuclear pores in a CRM1/RAN-dependent manner involving oxidative stress-mediated phosphorylation at Tyr-700. Dephosphorylation at this site by SHP2 retains TERT in the nucleus. Translocated to the nucleus by phosphorylation by AKT (By similarity). The primer grip sequence in the RT domain is required for telomerase activity and for stable association with short telomeric primers. The RNA-interacting domain 1 (RD1)/N-terminal extension (NTE) is required for interaction with the pseudoknot-template domain of each of TERC dimers. It contains anchor sites that bind primer nucleotides upstream of the RNA-DNA hybrid and is thus an essential determinant of repeat addition processivity (By similarity). The RNA-interacting domain 2 (RD2) is essential for both interaction with the CR4-CR5 domain of TERC and for DNA synthesis. Phosphorylation at Tyr-700 under oxidative stress leads to translocation of TERT to the cytoplasm and reduces its antiapoptotic activity. Dephosphorylated by SHP2/PTPN11 leading to nuclear retention. Phosphorylation at Ser-231 by the AKT pathway promotes nuclear location. Phosphorylation at the G2/M phase at Ser-450 by DYRK2 promotes ubiquitination by the EDVP complex and degradation (By similarity). Ubiquitinated by the EDVP complex, a E3 ligase complex following phosphorylation at Ser-450 by DYRK2. Ubiquitinated leads to proteasomal degradation (By similarity). Belongs to the reverse transcriptase family. Telomerase subfamily.