Telomerase

Literature References: RNA-containing enzyme found in unicellular organisms and germline cells. Also produced by tumor cells and by immortalized cell lines; not expressed in normal somatic cells. Specialized reverse transcriptase that adds short, tandemly repeated segments of DNA onto the ends of eukaryotic chromosomes (telomeres) using its RNA component as a template. Replenishes the small amount of telomeric DNA that is normally lost during replication. In the absence of telomerase, this incremental loss of DNA continues with each cell division until the chromosome can no longer replicate and ultimately results in cell death. Activation of telomerase is associated with the unlimited proliferation of tumor cells. Discovery in the ciliate, Tetrahymena thermophila: C. W. Greider, E. H. Blackburn, Cell 43, 405 (1985). Overview and potential physiological significance: C. W. Greider, BioEssays 12, 363-369 (1990). Proposed role in cell immortalization: C. M. Counter et al., EMBO J. 11, 1921 (1992). Detection in human ovarian carcinoma cells: idem et al., Proc. Natl. Acad. Sci. USA 91, 2900 (1994). Structural studies: A. Bhattacharyya, E. H. Blackburn, EMBO J. 13, 5721 (1994); M. McCormick-Graham, D. P. Romero, Nucleic Acids Res. 23, 1091 (1995). Clinical implications in cancer diagnosis and therapy: N. W. Kim, Eur. J. Cancer 33, 781 (1997). Effect on life-span of normal human cells in vitro: A. G. Bodnar et al., Science 279, 349 (1998).