Catalytic component of telomerase, an essential ribonucleoprotein enzyme that copies new telomeric repeats onto chromosome ends by repetitively synthesizing the short telomere-repeat sequence 5'-TTGGGG-3' using an RNA template component TER (PubMed:10944124, PubMed:15696174, PubMed:17322903, PubMed:20713447, PubMed:16462747). TERT is a reverse transcriptase that adds simple sequence repeats to chromosome ends by copying a template sequence within the RNA component of the enzyme (PubMed:10944124, PubMed:15696174, PubMed:17322903, PubMed:20713447, PubMed:16462747). a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Component of the telomerase holoenzyme complex, composed of the catalytic core (the catalytic subunit TERT, the telomerase RNA template component TER and TAP65/p65), which is associated with two heterotrimeric subcomplexes: (i) the replication protein A (RPA)-related subcomplex, composed of TEB1, RPA2/TEB2 and RPA3/TEB3 and (ii) the CST-like subcomplex, composed of TAP75/p75, TAP45/p45 and TAP19/p19 (PubMed:15696174, PubMed:17322903, PubMed:20713447, PubMed:19941821, PubMed:23552895, PubMed:26472759, PubMed:29775593). TEB1 and the CST-like subcomplex are tethered to the catalytic core by TAP50/p50 (PubMed:19941821, PubMed:23552895, PubMed:26472759, PubMed:29775593). Belongs to the reverse transcriptase family. Telomerase subfamily.