Telomeric repeat binding factor 2 (TRF2) folds human telomeres into loops to prevent unwanted DNA repair and chromosome end-joining. The N-terminal basic domain of TRF2 (B-domain) protects the telomeric displacement loop (D-loop) from cleavage by endonucleases. Repressor activator protein 1 (Rap1) binds TRF2 and improves telomeric DNA recognition. We found that the B-domain of TRF2 stabilized the D-loop and thus reduced unwinding by BLM and RPA, whereas the formation of the Rap1-TRF2 complex restored DNA unwinding. To understand how the B-domain of TRF2 affects DNA binding and D-loop processing, we analyzed DNA binding of full-length TRF2 and a truncated TRF2 construct lacking the B-domain. We quantified how the B-domain improves TRF2's interaction with DNA via enhanced long-range electrostatic interactions. We developed a structural envelope model of the B-domain bound on DNA. The model revealed that the B-domain is flexible in solution but becomes rigid upon binding to telomeric DNA. We proposed a mechanism for how the B-domain stabilizes the D-loop.

LifeB Chromatin Molecular Complexes CEITEC and Functional Genomics and Proteomics National Centre for Biomolecular Research Faculty of Science Masaryk University Brno CZ 62500 Czech Republic

Structural Biology of Gene Regulation CEITEC Masaryk University Brno CZ 62500 Czech Republic

Nucleic Acids Res. 2017 Dec 1;45(21):12599. doi: 10.1093/nar/gkx968. PubMed

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