title: The clustering of telomeres and colocalization with Rap1, Sir3, and Sir4 proteins in wild-type Saccharomyces cerevisiae.
abstract: We have developed a novel technique for combined immunofluorescence/in situ hybridization on fixed budding yeast cells that maintains the three-dimensional structure of the nucleus as monitored by focal sections of cells labeled with fluorescent probes and by staining with a nuclear pore antibody. Within the resolution of these immunodetection techniques, we show that proteins encoded by the SIR3, SIR4, and RAP1 genes colocalize in a statistically significant manner with Y' telomere-associated DNA sequences. In wild-type cells the Y' in situ hybridization signals can be resolved by light microscopy into fewer than ten foci per diploid nucleus. This suggests that telomeres are clustered in vegetatively growing cells, and that proteins essential for telomeric silencing are concentrated at their sites of action, i.e., at telomeres and/or subtelomeric regions. As observed for Rap1, the Sir4p staining is diffuse in a sir3- strain, and similarly, Sir3p staining is no longer punctate in a sir4- strain, although the derivatized Y' probe continues to label discrete sites in these strains. Nonetheless, the Y' FISH is altered in a qualitative manner in sir3 and sir4 mutant strains, consistent with the previously reported phenotypes of shortened telomeric repeats and loss of telomeric silencing.
authors.affiliation: Swiss Institute for Experimental Cancer Research, Epalinges/Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Gotta
authors.forename: T
authors.initials: T
authors.lastname: Laroche
authors.forename: A
authors.initials: A
authors.lastname: Formenton
authors.forename: L
authors.initials: L
authors.lastname: Maillet
authors.forename: H
authors.initials: H
authors.lastname: Scherthan
authors.forename: S M
authors.initials: SM
authors.lastname: Gasser
mesh_terms: D000918:Antibody Specificity; D015153:Blotting, Western; D002467:Cell Nucleus / Q000737:chemistry; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins / Q000032:analysis* / Q000235:genetics; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000235:genetics; D017404:In Situ Hybridization, Fluorescence; D009154:Mutation / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000502:physiology; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D016615:Telomere / Q000737:chemistry / Q000502:physiology*; D015534:Trans-Activators / Q000032:analysis* / Q000235:genetics; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics; D020668:rap GTP-Binding Proteins
chemical_list: D005656:Fungal Proteins; D012333:RNA, Messenger; C084122:SIR3 protein, S cerevisiae; C061573:SIR4 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; D014157:Transcription Factors; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins