DYNAMICS OF TRANSFER-RNA - EXPERIMENTAL NEUTRON-SPECTRA COMPARED WITHA NORMAL-MODE ANALYSIS

A comparison is made of experimental inelastic neutron scattering spec tra from tRNA with spectra calculated from a normal mode analysis of t he molecule. The experimental data indicate that a dynamic transition occurs with temperature, as is seen in proteins. At low temperatures a board peak is seen in the dynamic structure factor, due to the lowest frequency collective modes. This peak is centered at approximately 40 cm-1, somewhat higher in frequency than that observed in small globul ar proteins. The vibrational frequency distribution calculated from th e normal mode analysis rises to a broad maximum at 50 cm-1, in general accord with the experiment. However, the lowest frequency vibrations in the harmonic model (<40 cm-1) are not present in the experimental s ample. Possible reasons for this are discussed.