Telomerase is a ribonucleoprotein enzyme essential for the replication of chromosome termini in most eukaryotes. It elongates telomeres. It is a reverse transcriptase that adds simple sequence repeats to chromosome ends by copying a template sequence within the RNA component of the enzyme. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Catalytic subunit of the telomerase holoenzyme complex composed minimally of trt1 and the telomerase RNA template component (PubMed:24793650). Interacts with est1 (PubMed:12676088). Deletion causes telomere shortening and senescence. Belongs to the reverse transcriptase family. Telomerase subfamily.