An enzyme that preserves the length of telomeres across cell divisions in germ cells, stem cells, and most cancer cells. A kind of reverse transcriptase, telomerase is an RNA-containing enzyme that synthesizes the DNA of telomeres by reverse transcription. It is active during DNA replication and is thought to play a role in the proliferation and apparent immortality of cells in which it is present. In cells that lack telomerase (that is, in most somatic cells of the body), the telomeres of chromosomes shorten and eventually disappear over repeated cell divisions. The inhibition of telomerase is being investigated as a method of killing cancerous cells. See more at telomere.