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Telomerase is an enzyme which replicates the terminal sequences of eukaryotic chromosomes, namely the telomeres. Cells which have an unlimited replicative capacity such as male germ cells and the majority of human cancers have high levels of telomerase activity. The level and frequency of telomerase activity in more than 85% of all cancers highlights the critical role telomerase plays in tumor progression. Telomerase activation is the most common general marker for a cancer cell to date making it an attractive target for new cancer diagnostics and therapeutics. Human telomerase activity can be reconstituted in vitro by the essential RNA subunit, hTERC, and the catalytic protein component coded for by the hTERT gene. Both the human telomerase reverse transcriptase gene (hTERT) and the telomerase RNA gene (hTERC) are controlled at least in part at the transcriptional level. The hTERT gene is expressed at low levels in cancer cells and is generally undetectable in normal cells.
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