Studies of telomeric complexes by Nuclear Magnetic Resonance ; Etude de complexes télomériques par Résonance Magnétique Nucléaire

Telomeres are special nucleoprotein complexes at the end of eukaryotic chromosomes. Human telomeric DNA contains between 500 and 3000 repeats of the sequence d(T2AG3)n (G-strand) and of the complementary strand C3TA2 (C-strand). The G-strand forms at the end of telomeres a single strand overhang containing 50 to 200 nucleotides. Telomeres can switch stochastically between two states: capped and uncapped. Capping is functionally defined as preserving the physical integrity of the chromosomes. To explain this protection, the T-loop/D-loop model has been proposed. In this model, the 3'G single-stranded overhang is tucked back inside the double-stranded telomeric DNA resulting in a large T-loop that is stabilized by an intramolecular D-loop. Formation of these loops involved a lots of proteins, which are directly or indirectly bound to telomeric DNA. Two proteins, called TRF1 and TRF2, seem to have a very important role in the formation of the loops. However, the molecular mechanism of such T-loop/D-loop is speculative, especially the process that involves TRF2 protein. The work presented in this thesis reports the NMR studies of the DNA binding domain of the TRF2 protein (Myb domain) and its interactions with telomeric DNA, following by the studies of 4 D-loop models. After the determination of the structure and internal dlmamics studies of Myb-TRF2 domain, studies of two complexes involving Myb-TRF2 protein and telomeric DNA are presented. These studies allow us to have a better understànding of Myb-TRF2 role and show that this protein has a sequence specifity and binds only double stranded-DNA. Then, 4 different D-loop models have been studied by NMR to determine their three-dimensional structures. ; Les télomères sont des complexes nucléoprotéiques localisés à l'extrémité des chromosomes des cellules eucaryotes. L'ADN télomérique humain contient entre 500 et 3000 repétitions de la séquence d(T2AG3)n (brin-G) et de son brin complémentaire C3TA2 (brin-C). Le brin G est terminé par une extrémité simple brin ...