Crystal Structure of an Initiation Factor Bound to the 30S Ribosomal Subunit
Initiation of translation at the correct position on messenger RNA is essential for accurate protein synthesis. In prokaryotes, this process requires three initiation factors: IF1, IF2, and IF3. Here we report the crystal structure of a complex of IF1 and the 30S ribosomal subunit. Binding of IF1 occludes the ribosomal A site and flips out the functionally important bases A1492 and A1493 from helix 44 of 16S RNA, burying them in pockets in IF1. The binding of IF1 causes long-range changes in the conformation of H44 and leads to movement of the domains of 30S with respect to each other. The structure explains how localized changes at the ribosomal A site lead to global alterations in the conformation of the 30S subunit.
© 2001 American Association for the Advancement of Science. 27 November 2000; accepted 20 December 2000. We thank M. Pacold and J. Ogle for critical comments on the manuscript and R. Ravelli, S. McSweeney, and G. Leonard for help and advice during synchrotron data collection at ESRF, Grenoble, France. Supported by the Medical Research Council (U.K.) and grant GM 44973 from the NIH (S. W. White and V.R.) and by a Human Frontier Science Program long-term postdoctoral fellowship (D.E.B.) and an NIH predoctoral fellowship (W.M.C.). Coordinates have been deposited in the Protein Data Bank with the accession number 1HR0.