SMALL-ANGLE SCATTERING IN RIBOSOMAL STRUCTURE RESEARCH - LOCALIZATIONOF THE MESSENGER-RNA WITHIN RIBOSOMAL ELONGATION STATES

Besides EM and biochemical studies small angle scattering (SAS) examin ations have contributed significantly to our current knowledge about t he ribosomal structure. SAS does not only allow the validation of comp eting models but permits independent model building. However, the majo r contribution of SAS to ribosomal structure research derived from its ability to reveal the spatial distribution of the individual ribosoma l components (57 in the E. coli ribosome) within the ribosomal structu re. More recently, an improved scattering method (proton-spin contrast variation) made it possible also to address the question of mapping f unctional ligands in defined ribosomal elongation states. Here, we rev iew the contributions of SAS to the current understanding of the ribos ome. Furthermore we present the direct localization of a small mRNA fr agment within 70S elongation complexes and describe its movement upon the translocation reaction. The successful mapping of this fragment co mprising only about 0.6% of the total mass of the complex proves that proton-spin contrast-variation is a powerful tool in modern ribosome r esearch.