Published online 19 April 2004
Nucleic Acids Research, 2004, Vol. 32, No. 7 2171-2180
© 2004 Oxford University Press
Human telomerase catalyzes nucleolytic primer cleavage
Department of Anatomy and Cell Biology, McGill University, Montréal, Québec H3A 2B4, Canada and 1 Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montréal, Québec H3T 1E2, Canada
*To whom correspondence should be addressed. Tel: +1 514 340 8260; Fax: +1 514 340 8295; Email: chantal.autexier{at}mcgill.ca
Received February 16, 2004; Revised and Accepted March 24, 2004
Telomerase is a reverse transcriptase that uses an integral RNA molecule to add de novo G-rich repeats onto telomeric DNA, or onto nontelomeric DNA generated during chromosome fragmentation and breakage events. A telomerase-mediated DNA substrate cleavage activity has been reported in ciliates and yeasts. Nucleolytic cleavage may serve a proofreading function, enhance processivity or ensure that nontemplate telomerase RNA sequences are not copied into DNA. We identified and characterized a human telomerase-mediated nucleolytic cleavage activity using enzyme reconstituted in a rabbit reticulocyte lysate in vitro transcription/translation system and native enzyme extracted from cells. We found that telomerase catalyzed the removal of nucleotides from DNA substrates including those that can form a mismatch with the RNA template or that contain nontelomeric sequences located 3' to a telomeric sequence. Unlike Tetrahymena telomerase, human telomerase catalyzed the removal of more than one nucleotide (up to 13) from telomeric primers. DNA substrates predicted to align at the 3'-end of the RNA template were not cleaved, consistent with cleavage being dictated by the template 5'-end. We also found some differences in the nuclease activity between RRL-reconstituted human telomerase and native enzyme.
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