Structural polymorphism of telomeres studied by photon correlation spectroscopy

Photon Correlation spectroscopy (PCS) was used to study the dynamics and st ructure of Tetrahymena telomeric sequence d(5'-TGGGGT-3')(4). Two different modes were observed, corresponding to the following structures: intermolec ular (tetramolecular) G-quadruplex and intramolecular (monomeric) G-quartet . Experimental values of translational diffusion coefficients D-T were obta ined for each structural form. The value of D-T for the monomer equals to 1 .4 x 10(6)(cm(2)/s), while for the tetramolecular structure, to 0.8 x 106(c m(2)/s). The relative weight concentrations of these two forms were analyze d versus the concentration of NaCl varied from 10 mM to 500 mM. The values of experimentally determined diffusion coefficients were compared with thos e calculated assuming the "bead model" and with the atomic coordinates from the NMR and X-ray crystallographic data. For both structures the experimen tal and calculated values of D-T were in reasonable agreement. In the entir e NaCl concentration range studied, the contribution of the relative weight concentration of the monomeric telomere form changed from 85% for 10 mM Na Cl to 60% for 500 mM NaCl.