title: TRF1 and TRF2 use different mechanisms to find telomeric DNA but share a novel mechanism to search for protein partners at telomeres.
abstract: Human telomeres are maintained by the shelterin protein complex in which TRF1 and TRF2 bind directly to duplex telomeric DNA. How these proteins find telomeric sequences among a genome of billions of base pairs and how they find protein partners to form the shelterin complex remains uncertain. Using single-molecule fluorescence imaging of quantum dot-labeled TRF1 and TRF2, we study how these proteins locate TTAGGG repeats on DNA tightropes. By virtue of its basic domain TRF2 performs an extensive 1D search on nontelomeric DNA, whereas TRF1's 1D search is limited. Unlike the stable and static associations observed for other proteins at specific binding sites, TRF proteins possess reduced binding stability marked by transient binding (∼ 9-17 s) and slow 1D diffusion on specific telomeric regions. These slow diffusion constants yield activation energy barriers to sliding ∼ 2.8-3.6 κ(B)T greater than those for nontelomeric DNA. We propose that the TRF proteins use 1D sliding to find protein partners and assemble the shelterin complex, which in turn stabilizes the interaction with specific telomeric DNA. This 'tag-team proofreading' represents a more general mechanism to ensure a specific set of proteins interact with each other on long repetitive specific DNA sequences without requiring external energy sources.
authors.affiliation: Physics Department, North Carolina State University, Raleigh, NC 27695, USA, Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15219, USA, Electric and Computer Engineering Department, University of North Carolina at Charlotte, Charlotte, NC 28223, USA, Department of Industrial and System Engineering, North Carolina State University, Raleigh, NC 27695, USA, Department of Cell Biology, Center for Biologic Imaging, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15219, USA, Division of Biophysics, Universität Osnabrück, Barbarstrasse 11, 49076, Osnabrück, Germany and School of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ UK.
authors.forename: Jiangguo
authors.initials: J
authors.lastname: Lin
authors.forename: Preston
authors.initials: P
authors.lastname: Countryman
authors.forename: Noah
authors.initials: N
authors.lastname: Buncher
authors.forename: Parminder
authors.initials: P
authors.lastname: Kaur
authors.forename: Longjiang
authors.initials: L
authors.lastname: E
authors.forename: Yiyun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Greg
authors.initials: G
authors.lastname: Gibson
authors.forename: Changjiang
authors.initials: C
authors.lastname: You
authors.forename: Simon C
authors.initials: SC
authors.lastname: Watkins
authors.forename: Jacob
authors.initials: J
authors.lastname: Piehler
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Opresko
authors.forename: Neil M
authors.initials: NM
authors.lastname: Kad
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
mesh_terms: D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004058:Diffusion; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012091:Repetitive Sequences, Nucleic Acid; D016615:Telomere / Q000737:chemistry / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1 / Q000378:metabolism*; D035341:Telomeric Repeat Binding Protein 2 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; D004247:DNA