Molecular mechanisms of DNA end-loop formation by TRF2.
In the telomere region of human chromosomes, the (TTAGGG)n sequence stretches over several kilobases and forms a distinct higher-order structure with various proteins. Telomere repeat binding factors (TRFs) bind specifically to this sequence and play critical roles in the maintenance of telomere structure and function. Here, we prepared a series of linear DNA carrying a stretch of telomeric sequence ((TTAGGG)n, approximately 1.8 (kb) with different end-structures and observed their higher-order complexes with TRFs by atomic force microscopy. TRF2 molecules exclusively bound to the telomeric DNA region at several different places simultaneously mainly as a dimer, and often mediated DNA loop formation by forming a tetramer at the root. These multiple-binding, multimerization and DNA loop formation by TRF2 were observed regardless of the DNA-end structure (blunt, 3'-overhanging, telomeric, non-telomeric). However, when the DNA end carried the telomeric-3'-overhanging region, the loop was frequently formed at the end of the DNA. Namely, the TRF2-mediated DNA loop formation is independent of the end-structure and the 3'-overhanging TTAGGG sequence is responsible for the stabilization of the loop. TRF1 also bound to the telomeric DNA as a dimer, but did not mediate DNA loop formation by itself. These results provide a new insight into the molecular mechanism of DNA end-loop formation by TRFs.
Department of Responses to Environmental Signals and Stresses, Graduate School of Biostudies, Kyoto University, Kitashirawkawa-oiwake-cho Sakyo-ku Kyoto, 606-8502, Japan. yoshimura@lif.kyoto-u.ac.jp
Shige H
SH
Yoshimura
Hugo
H
Maruyama
Fuyuki
F
Ishikawa
Rieko
R
Ohki
Kunio
K
Takeyasu
D001665:Binding Sites; D002877:Chromosomes, Human / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D019281:Dimerization; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D018625:Microscopy, Atomic Force; D011108:Polymers / Q000737:chemistry / Q000378:metabolism; D016615:Telomere / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D035341:Telomeric Repeat Binding Protein 2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D011108:Polymers; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; D004247:DNA