Telomerase

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Telomerase, also called terminal transferase,^[1] is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. A telomere is a region of repetitive sequences at each end of the chromosomes of most eukaryotes. Telomeres protect the end of the chromosome from DNA damage or from fusion with neighbouring chromosomes. The fruit fly Drosophila melanogaster lacks telomerase, but instead uses retrotransposons to maintain telomeres.^[2]

Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule (e.g., with the sequence 3′-CCCAAUCCC-5′ in Trypanosoma brucei)^[3] which is used as a template when it elongates telomeres. Telomerase is active in gametes and most cancer cells, but is normally absent in most somatic cells.