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Molecular and Cellular Biology, November 2001, p. 7277-7286, Vol. 21, No. 21
Swiss Institute for Experimental Cancer
Research (ISREC), CH-1066 Epalinges, Switzerland
Received 24 April 2001/Returned for modification 15 June
2001/Accepted 2 August 2001
Telomerase is a ribonucleoprotein enzyme that adds repetitive
sequences to the ends of linear chromosomes, thereby counteracting nucleotide loss due to incomplete replication. A short region of the
telomerase RNA subunit serves as template for nucleotide addition onto
the telomere 3' end. Although Saccharomyces cerevisiae contains only one telomerase RNA gene, telomere repeat sequences are
degenerate in this organism. Based on a detailed analysis of the
telomere sequences specified by wild-type and mutant RNA templates in
vivo, we show that the divergence of telomere repeats is due to
abortive reverse transcription in the 3' and 5' regions of the template
and due to the alignment of telomeres in multiple registers within the
RNA template. Through the interpretation of wild-type telomere
sequences, we identify nucleotides in the template that are not
accessible for base pairing during substrate annealing. Rather, these
positions become available as templates for reverse transcription only
after alignment with adjacent nucleotides has occurred, indicating that
a conformational change takes place upon substrate binding. We also
infer that the central part of the template region is reverse
transcribed processively. The inaccessibility of certain template
positions for alignment and the processive polymerization of the
central template portion may serve to reduce the possible repeat
diversification and enhance the incorporation of binding sites for
Rap1p, the telomere binding protein of budding yeast.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.21.7277-7286.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Molecular Basis for Telomere Repeat Divergence in
Budding Yeast
*
Correspondent footnote. Mailing address: Swiss
Institute for Experimental Cancer Research (ISREC), Chemin des
Boveresses 155, CH-1066 Epalinges, Switzerland. Phone: 41-21-6925912. Fax: 41-21-6526933. E-mail:
joachim.lingner{at}isrec.unil.ch.
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