Determination of RNA tertiary structure by Electron Paramagnetic Resonance Spectroscopy (EPR)

Since the discovery of ribozymes in 1980, RNA is no longer considered only as a transporter of the genetic information but also as a participating molecule in each step of the gene expression. RNA can form complex three dimensional structures designed to perform specific functions. These structures are highly dependent on the presence of metal ions but few have been already solved. In the last few years the Electron Paramagnetic Resonance (EPR) spectroscopy has enabled a real improvement in the determination of proteins' conformation([1]) but few studies have been performed on nucleic acids.([2]) Indeed EPR enables to gain structural (distances between 15 and 60Angstrom can be measured) and dynamic data (motions which occur on a timescale from millisecond to nanosecond can be analysed). Our aim is to test this method on the well known Hammerhead Ribozyme, whose X-ray structure has been entirely determined in 1994:31 it is composed of one core and three helices, whose orientation depends on the magnesium concentration. Besides the magnesium ions are involved in the mechanism of substrate's self-cleavage.