Dr. Joachim Frank
Howard Hughes Medical Institute
Albany, New York

Monday, February 27, 2006
3:00 pm (CT)
3269 Beckman Institute

Abstract

Cryo-electron microscopy of single (i.e., unattached) particles combined with 3D reconstruction offers a way to visualize molecular machines in successive states of processing under native conditions. Using this technique, we are studying the mechanism of translation, by the ribosome, of the genetic information residing on the mRNA into a polypeptide chain that eventually folds into a protein. To trap ribosome complexes (consisting of ribosome with ligands such as tRNA and elongation factors) in defined states, we use antibiotics or nonhydrolyzable GTP analogs. Tens of thousand or sometimes over 100,000 ribosome images go into a typical reconstruction, and the resolution of the resulting density maps is in the range of 7-12 Å. “Quasi-atomic” models can be obtained by flexible fitting and docking of X-ray structures into the density maps. I will describe some of the maps obtained for the two key processes during the elongation cycle, decoding and translocation, and what we have learned from a comparison of these maps.