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Science 21 August 2009:
Vol. 325. no. 5943, pp. 1014 - 1017
DOI: 10.1126/science.1175275
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Reports

Structures of the Ribosome in Intermediate States of Ratcheting

Wen Zhang,1,* Jack A. Dunkle,1,* Jamie H. D. Cate1,2,{dagger}

Protein biosynthesis on the ribosome requires repeated cycles of ratcheting, which couples rotation of the two ribosomal subunits with respect to each other, and swiveling of the head domain of the small subunit. However, the molecular basis for how the two ribosomal subunits rearrange contacts with each other during ratcheting while remaining stably associated is not known. Here, we describe x-ray crystal structures of the intact Escherichia coli ribosome, either in the apo-form (3.5 angstrom resolution) or with one (4.0 angstrom resolution) or two (4.0 angstrom resolution) anticodon stem-loop tRNA mimics bound, that reveal intermediate states of intersubunit rotation. In the structures, the interface between the small and large ribosomal subunits rearranges in discrete steps along the ratcheting pathway. Positioning of the head domain of the small subunit is controlled by interactions with the large subunit and with the tRNA bound in the peptidyl-tRNA site. The intermediates observed here provide insight into how tRNAs move into the hybrid state of binding that precedes the final steps of mRNA and tRNA translocation.

1 Departments of Molecular and Cell Biology and Chemistry, University of California at Berkeley, Berkeley, CA 94720, USA.
2 Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: jcate{at}lbl.gov

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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