title: The effect of the TRF2 N-terminal and TRFH regions on telomeric G-quadruplex structures.
abstract: The sequence of human telomeric DNA consists of tandem repeats of 5'-d(TTAGGG)-3'. This guanine-rich DNA can form G-quadruplex secondary structures which may affect telomere maintenance. A current model for telomere protection by the telomere-binding protein, TRF2, involves the formation of a t-loop which is stabilized by a strand invasion-like reaction. This type of reaction may be affected by G-quadruplex structures. We analyzed the influence of the arginine-rich, TRF2 N-terminus (TRF2(B)), as well as this region plus the TRFH domain of TRF2 (TRF2(BH)), on the structure of G-quadruplexes. Circular dichroism results suggest that oligonucleotides with 4, 7 and 8 5'-d(TTAGGG)-3' repeats form hybrid structures, a mix of parallel/antiparallel strand orientation, in K(+). TRF2(B) stimulated the formation of parallel-stranded structures and, in some cases, intermolecular structures. TRF2(BH) also stimulated intermolecular but not parallel-stranded structures. Only full-length TRF2 and TRF2(BH) stimulated uptake of a telomeric single-stranded oligonucleotide into a plasmid containing telomeric DNA in the presence of K(+). The results in this study suggest that G-quadruplex formation inhibits oligonucleotide uptake into the plasmid, but the inhibition can be overcome by TRF2. This study is the first analysis of the effects of TRF2 domains on G-quadruplex structures and has implications for the role of G-quadruplexes and TRF2 in the formation of t-loops.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami Miller School of Medicine, Miami, FL 33101-6129, USA.
authors.forename: Ilene M
authors.initials: IM
authors.lastname: Pedroso
authors.forename: William
authors.initials: W
authors.lastname: Hayward
authors.forename: Terace M
authors.initials: TM
authors.lastname: Fletcher
mesh_terms: D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry; D024202:Electrophoretic Mobility Shift Assay; D054856:G-Quadruplexes; D006801:Humans; D007700:Kinetics; D009841:Oligonucleotides / Q000737:chemistry / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011188:Potassium / Q000737:chemistry; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000737:chemistry; D016615:Telomere / Q000737:chemistry*; D035341:Telomeric Repeat Binding Protein 2 / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009841:Oligonucleotides; D010455:Peptides; D035341:Telomeric Repeat Binding Protein 2; D004247:DNA; D012964:Sodium; D011188:Potassium