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Molecular and Cellular Biology, May 2004, p. 3720-3733, Vol. 24, No. 9
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.9.3720-3733.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Functional Organization of Repeat Addition Processivity and DNA Synthesis Determinants in the Human Telomerase Multimer

Tara J. Moriarty,1,2 Delphine T. Marie-Egyptienne,1,2 and Chantal Autexier1,2,3*

Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital,1 Department of Anatomy and Cell Biology,2 Department of Medicine, McGill University, Montréal, Québec, Canada3

Received 22 September 2003/ Returned for modification 28 October 2003/ Accepted 4 February 2004

Human telomerase is a multimer containing two human telomerase RNAs (hTRs) and most likely two human telomerase reverse transcriptases (hTERTs). Telomerase synthesizes multiple telomeric repeats using a unique repeat addition form of processivity. We investigated hTR and hTERT sequences that were essential for DNA synthesis and processivity using a direct primer extension telomerase assay. We found that hTERT consists of two physically separable functional domains, a polymerase domain containing RNA interaction domain 2 (RID2), reverse transcriptase (RT), and C-terminal sequences, and a major accessory domain, RNA interaction domain 1 (RID1). RID2 mutants defective in high-affinity hTR interactions and an RT catalytic mutant exhibited comparable DNA synthesis defects. The RID2-interacting hTR P6.1 helix was also essential for DNA synthesis. RID1 interacted with the hTR pseudoknot-template domain and hTERT's RT motifs and putative thumb and was essential for processivity, but not DNA synthesis. The hTR pseudoknot was essential for processivity, but not DNA synthesis, and processivity was reduced or abolished in dimerization-defective pseudoknot mutants. trans-acting hTERTs and hTRs complemented the processivity defects of RID1 and pseudoknot mutants, respectively. These data provide novel insight into the catalytic organization of the human telomerase complex and suggest that repeat addition processivity is one of the major catalytic properties conferred by telomerase multimerization.

* Corresponding author. Mailing address: Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, 3755 Cote Ste. Catherine Road, Montréal, Québec, Canada H3T 1E2. Phone: (514) 340-8260. Fax: (514) 340-8295. E-mail: chantal.autexier{at}mcgill.ca.

Molecular and Cellular Biology, May 2004, p. 3720-3733, Vol. 24, No. 9
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.9.3720-3733.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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