Telomerase is an RNA-dependent DNA polymerase that uses an RNA component to add telomeric repeat sequences at the ends of chromosomes. Besides the RNA component which serves as the template that specifies the telomeric repeat, the telomerase complex contains a reverse transcriptase protein (TRT) and various accessory proteins including the telomerase-associated protein 1 (TEP1). Telomerase activity is low in most somatic cells, causing the gradual shortening of telomeres which can ultimately lead to telomere fusion and cell death. High levels of telomerase activity are widely seen in cancerous cells and while recent experiments have suggested that telomerase may be a viable target in cancer therapy, expression levels of TEP1 do not correlate with malignancy. At least two isoforms of TP1 are known to exist.