title: Analysis of telomerase in Candida albicans: potential role in telomere end protection.
abstract: Telomerase is a ribonucleoprotein reverse transcriptase responsible for the maintenance of one strand of telomere terminal repeats. Analysis of the telomerase complex in the budding yeast Saccharomyces cerevisiae has revealed the presence of one catalytic protein subunit (Est2p/TERT) and at least two noncatalytic components (Est1p and Est3p). The genome of the pathogenic yeast Candida albicans contains putative orthologues of all three telomerase components. Disruption of each homologue resulted in significant but distinct telomere dysfunction in Candida: Similar to S. cerevisiae, the Candida EST3 disruption strain exhibits progressive telomere loss over many generations, at a rate that is consistent with incomplete replication. In contrast, telomeres in both the Candida TERT and EST1 disruption strains can contract rapidly, followed by partial or nearly complete recovery, suggesting a defect in telomere "capping." We propose that these two telomerase subunits may participate in the protection of chromosomal ends in Candida: Analysis of telomerase-mediated primer extension in vitro indicates that only the TERT protein is absolutely essential for enzyme activity. Our results support the conservation of telomerase protein components beyond the catalytic subunit but reveal species-specific phenotypic alterations in response to loss of individual telomerase component. We also identify potential homologues of Est1p in phylogenetically diverse organisms. The Est1p sequence family possesses a conserved N-terminal domain predicted to be structurally related to tetratricopeptide repeat-containing proteins.
authors.affiliation: Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, New York, New York 10021, USA.
authors.forename: Sunitha M
authors.initials: SM
authors.lastname: Singh
authors.forename: Olga
authors.initials: O
authors.lastname: Steinberg-Neifach
authors.forename: I Saira
authors.initials: IS
authors.lastname: Mian
authors.forename: Neal F
authors.initials: NF
authors.lastname: Lue
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002176:Candida albicans / Q000201:enzymology*; D017124:Conserved Sequence; D004268:DNA-Binding Proteins; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D005656:Fungal Proteins; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; C099024:EST1 protein, S cerevisiae; C491580:EST3 protein, S cerevisiae; D019098:Telomerase