Study on conformational states of Escherichia coli tRNAPhe in solution by a modulation-free ESR-spectrometer

A modulation free Electron Spin Resonance spectrometer was used for the registration of spectral absorption lines of a spin-labeled Escherichia coli phenylalanine tRNA in solution with low (less than 0.1%) line shape distortion. The analysis of line shape of two different spin-labels introduced into position 8 revealed that phenylalanine tRNA in solution exists as a mixture of two conformers, the equilibria between conformers being dependent on pH, concentration of magnesium and functional state of tRNA (deacylated, aminoacylated or peptidylated). There are no overall structural rearrangements upon aminoacylation or peptidylation of tRNA. The observed small changes of spectral line shape can be assigned to shifts in conformational equilibria.