title: Functional conservation of the telomerase protein Est1p in humans.
abstract: Eukaryotic telomerase contains a telomerase reverse transcriptase (TERT) and an RNA template component that are essential for telomerase catalytic activity and several other telomerase-associated factors of which only a few appear to be integral enzyme components [1-3]. The first essential telomerase protein identified was S. cerevisiae Est1p, whose deletion leads to ever-shorter telomeres despite the persistence of telomerase activity [4-6]. Extensive genetic and biochemical data show that Est1p, via its interaction with the telomerase RNA and telomere end DNA binding complex Cdc13p/Stn1p/Ten1p, promotes the ability of telomerase to elongate telomeres in vivo [7-22]. The characterization of Est1p homologs outside of yeast has not been documented. We report the characterization of two putative human homologs of Est1p, hEST1A and hEST1B. Both proteins specifically associated with telomerase activity in human cell extracts and bound hTERT in rabbit reticulocyte lysates independently of the telomerase RNA. Overproduction of hEST1A cooperated with hTERT to lengthen telomeres, an effect that was specific to cells containing telomerase activity. Like Est1p, hEST1A (but not hEST1B) exhibited a single-stranded telomere DNA binding activity. These results suggest that the telomerase-associated factor Est1p is evolutionarily conserved in humans.
authors.affiliation: Ontario Cancer Institute/Advanced Medical Discovery Institute, University of Toronto, 620 University Avenue, Toronto, Ontario M5G 2C1, Canada.
authors.forename: Bryan E
authors.initials: BE
authors.lastname: Snow
authors.forename: Natalie
authors.initials: N
authors.lastname: Erdmann
authors.forename: Jennifer
authors.initials: J
authors.lastname: Cruickshank
authors.forename: Hartt
authors.initials: H
authors.lastname: Goldman
authors.forename: R Montgomery
authors.initials: RM
authors.lastname: Gill
authors.forename: Murray O
authors.initials: MO
authors.lastname: Robinson
authors.forename: Lea
authors.initials: L
authors.lastname: Harrington
mesh_terms: D015153:Blotting, Western; D002457:Cell Extracts / Q000737:chemistry; D015342:DNA Probes; D004268:DNA-Binding Proteins; D024202:Electrophoretic Mobility Shift Assay; D019143:Evolution, Molecular; D006801:Humans; D011233:Precipitin Tests; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D016415:Sequence Alignment; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism
chemical_list: D002457:Cell Extracts; D015342:DNA Probes; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C099024:EST1 protein, S cerevisiae; C509186:TERT protein, human; D019098:Telomerase