title: Rap1 in Candida albicans: an unusual structural organization and a critical function in suppressing telomere recombination.
abstract: Rap1 (repressor activator protein 1) is a conserved multifunctional protein initially identified as a transcriptional regulator of ribosomal protein genes in Saccharomyces cerevisiae but subsequently shown to play diverse functions at multiple chromosomal loci, including telomeres. The function of Rap1 appears to be evolutionarily plastic, especially in the budding yeast lineages. We report here our biochemical and molecular genetic characterizations of Candida albicans Rap1, which exhibits an unusual, miniaturized domain organization in comparison to the S. cerevisiae homologue. We show that in contrast to S. cerevisiae, C. albicans RAP1 is not essential for cell viability but is critical for maintaining normal telomere length and structure. The rap1 null mutant exhibits drastic telomere-length dysregulation and accumulates high levels of telomere circles, which can be largely attributed to aberrant recombination activities at telomeres. Analysis of combination mutants indicates that Rap1 and other telomere proteins mediate overlapping but nonredundant roles in telomere protection. Consistent with the telomere phenotypes of the mutant, C. albicans Rap1 is localized to telomeres in vivo and recognizes the unusual telomere repeat unit with high affinity and sequence specificity in vitro. The DNA-binding Myb domain of C. albicans Rap1 is sufficient to suppress most of the telomere aberrations observed in the null mutant. Notably, we were unable to detect specific binding of C. albicans Rap1 to gene promoters in vivo or in vitro, suggesting that its functions are more circumscribed in this organism. Our findings provide insights on the evolution and mechanistic plasticity of a widely conserved and functionally critical telomere component.
authors.affiliation: Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, 1300 York Ave., New York, New York 10021, USA.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Yu
authors.forename: Wei-Feng
authors.initials: WF
authors.lastname: Yen
authors.forename: Olga
authors.initials: O
authors.lastname: Steinberg-Neifach
authors.forename: Neal F
authors.initials: NF
authors.lastname: Lue
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002176:Candida albicans / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D017434:Protein Structure, Tertiary; D011995:Recombination, Genetic; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D000089804:Shelterin Complex; D013045:Species Specificity; D016615:Telomere / Q000235:genetics* / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D004271:DNA, Fungal; D005656:Fungal Proteins; C474965:RAP1 protein, Candida albicans; C440829:RAP1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; D014157:Transcription Factors