title: TRF1 binds a bipartite telomeric site with extreme spatial flexibility.
abstract: TRF1 is a key player in telomere length regulation. Because length control was proposed to depend on the architecture of telomeres, we studied how TRF1 binds telomeric TTAGGG repeat DNA and alters its conformation. Although the single Myb-type helix-turn-helix motif of a TRF1 monomer can interact with telomeric DNA, TRF1 predominantly binds as a homodimer. Systematic Evolution of Ligands by Exponential enrichment (SELEX) with dimeric TRF1 revealed a bipartite telomeric recognition site with extreme spatial variability. Optimal sites have two copies of a 5'-YTAGGGTTR-3' half-site positioned without constraint on distance or orientation. Analysis of binding affinities and DNase I footprinting showed that both half-sites are simultaneously contacted by the TRF1 dimer, and electron microscopy revealed looping of the intervening DNA. We propose that a flexible segment in TRF1 allows the two Myb domains of the homodimer to interact independently with variably positioned half-sites. This unusual DNA binding mode is directly relevant to the proposed architectural role of TRF1.
authors.affiliation: The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
authors.forename: A
authors.initials: A
authors.lastname: Bianchi
authors.forename: R M
authors.initials: RM
authors.lastname: Stansel
authors.forename: L
authors.initials: L
authors.lastname: Fairall
authors.forename: J D
authors.initials: JD
authors.lastname: Griffith
authors.forename: D
authors.initials: D
authors.lastname: Rhodes
authors.forename: T
authors.initials: T
authors.lastname: de Lange
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D020836:Protein Structure, Quaternary; D020598:Proto-Oncogene Proteins c-myb / Q000737:chemistry / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D008024:Ligands; D020598:Proto-Oncogene Proteins c-myb; D035321:Telomeric Repeat Binding Protein 1; D004247:DNA