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Molecular and Cellular Biology, December 2003, p. 8440-8449, Vol. 23, No. 23
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.23.8440-8449.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

A Conserved Telomerase Motif within the Catalytic Domain of Telomerase Reverse Transcriptase Is Specifically Required for Repeat Addition Processivity

Neal F. Lue,1* You-Chin Lin,1 and I. Saira Mian2

Department of Microbiology & Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, New York, New York 10021,1 Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 947202

Received 16 July 2003/ Returned for modification 1 August 2003/ Accepted 22 August 2003

Telomerase is a ribonucleoprotein reverse transcriptase responsible for the maintenance of one strand of the telomere terminal repeats. The catalytic protein subunit of the telomerase complex, known as TERT, possesses a reverse transcriptase (RT) domain that mediates nucleotide addition. The RT domain of TERT is distinguishable from retroviral and retrotransposon RTs in having a sizable insertion between conserved motifs A and B', within the so-called fingers domain. Sequence analysis revealed the existence of conserved residues in this region, named IFD (insertion in fingers domain). Mutations of some of the conserved residues in Saccharomyces cerevisiae TERT (Est2p) abolished telomerase function in vivo, testifying to their importance. Significant effects of the mutations on telomerase activity in vitro were observed, with most of the mutants exhibiting a uniform reduction in activity regardless of primer sequence. Remarkably, one mutant manifested a primer-specific defect, being selectively impaired in extending primers that form short hybrids with telomerase RNA. This mutant also accumulated products that correspond to one complete round of repeat synthesis, implying an inability to effect the repositioning of the DNA product relative to the RNA template that is necessary for multiple repeat addition. Our results suggest that the ability to stabilize short RNA-DNA hybrids is crucial for telomerase function in vivo and that this ability is mediated in part by a more elaborate fingers domain structure.

* Corresponding author. Mailing address: Department of Microbiology & Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021. Phone: (212) 746-6506. Fax: (212) 746-8587. E-mail: nflue{at}med.cornell.edu.

Molecular and Cellular Biology, December 2003, p. 8440-8449, Vol. 23, No. 23
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.23.8440-8449.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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