title: Functional organization of repeat addition processivity and DNA synthesis determinants in the human telomerase multimer.
abstract: 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.
authors.affiliation: Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital and Department of Anatomy and Cell Biology, McGill University, Montréal, Québec, Canada.
authors.forename: Tara J
authors.initials: TJ
authors.lastname: Moriarty
authors.forename: Delphine T
authors.initials: DT
authors.lastname: Marie-Egyptienne
authors.forename: Chantal
authors.initials: C
authors.lastname: Autexier
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001483:Base Sequence; D020134:Catalytic Domain; D004261:DNA Replication; D004268:DNA-Binding Proteins; D006801:Humans; D046911:Macromolecular Substances; D009687:Nuclear Proteins / Q000378:metabolism; D000078723:Nuclear Receptor Interacting Protein 1; D009690:Nucleic Acid Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D019098:Telomerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D000078723:Nuclear Receptor Interacting Protein 1; D019098:Telomerase