Telomerase !

Telomerase lengthens chromosome ends (telomeres) using its own RNA as a template; it is active in stem cells and in most cancers.

Updated 2026-11-01

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Key facts

It is a reverse transcriptase: the TERT protein + the TERC (hTR) template RNA, which holds the sequence complementary to the repeat.
It adds TTAGGG repeats to the 3' end of the G-rich strand.
It solves the 'end-replication problem': without it telomeres shorten with each division.
Active in germ cells, stem cells and about 85–90% of cancers; almost off in adult somatic cells.
Very short telomeres → senescence or apoptosis (Hayflick limit).

TERT transcription is the limiting step; TERT promoter mutations switch it on in melanoma, glioblastoma and bladder cancer.
The protective shelterin complex (TRF1, TRF2, POT1, TPP1) recruits telomerase and limits its access to the telomere.
Dyskerin (DKC1) stabilises telomerase RNA.

Imetelstat (an oligonucleotide against the RNA template; used in some myeloid neoplasms)

Short-telomere syndromes (dyskeratosis congenita: dystrophic nails, leukoplakia, reticular pigmentation), with bone marrow failure and pulmonary fibrosis.
TERT and TERC variants are found in part of familial idiopathic pulmonary fibrosis.
Its reactivation lets tumour cells divide without limit: a hallmark of cancer.

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Why is telomerase a reverse transcriptase?

It uses its own RNA (TERC) as a template to make DNA: it copies RNA into DNA.

Which sequence does human telomerase add?

TTAGGG repeats at the 3' end of the telomere's G-rich strand.

Why do most cancer cells reactivate telomerase?

To stop their telomeres shortening into senescence, so they can divide without limit.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: TERT: Telomerase reverse transcriptase (human) (UniProt, 2026); TERT gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); 9SHZ: Cryo-EM structure of the catalytic core of human telomerase at the elongation state of the repeat addition cycle (RCSB Protein Data Bank, 2026); Telomere Maintenance (Reactome, 2026); Telomere (National Human Genome Research Institute (NHGRI), 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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