Structural dynamics of bacterial ribosomes: I. Characterization of vacant couples and their relation to complexed ribosomes

doi:10.1016/0022-2836(73)90021-1

Journal of Molecular Biology

Volume 75, Issue 2, 5 April 1973, Pages 281-294

https://doi.org/10.1016/0022-2836(73)90021-1 Get rights and content

Abstract

Ribosomes not engaged in protein synthesis (vacant couples), in contrast to complexed ribosomes bearing nascent chains, dissociate during sedimentation in sucrose gradients at high g forces and at Mg²⁺ concentrations below 15 mm. As a result of this dissociation, a new peak between the 70 S complexed ribosomes and the free 50 S subunits is observed, the position of which shifts from about 55 S to 70 S as the Mg²⁺ concentration in the gradient is raised from 5 to 15 mm. The apparent 60 S peak consists of 50 S subunits produced during dissociation in the gradient. At low g forces, the sedimentation rate of complexed and vacant ribosomes is indistinguishable, even at 5 mm-Mg²⁺. These sedimentation properties are valid criteria to differentiate vacant and complexed ribosomes. This is shown by converting complexed ribosomes quantitatively into vacant couples by removing the nascent chains through termination release or with puromycin, or by converting vacant couples into initiation complexes with R17 RNA, fMet-tRNA and initiation factors.

Ribosomes from cells harvested by slow cooling consist almost entirely of vacant couples, all of which are active in protein synthesis with natural messengers. The structural features responsible for the interaction between subunits are discussed.

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^☆: This work was supported by Research grant no. P381F from the American Cancer Society and grant no. 5RO1CA11797 to one of us (H. N.) from the U.S. Public Health Service. One of us (M. H. S.) was supported in part by the Deutsche Forschungsgemeinschaft. This work is submitted as partial fulfillment of a doctoral thesis by one of us (M. N.). One author (H. N.) is a Career Professor of the American Cancer Society.

^†: Present address: Dept. of Biochemistry, Biozentrum University of Basel, Basel, Switzerland.

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Journal of Molecular Biology

Structural dynamics of bacterial ribosomes: I. Characterization of vacant couples and their relation to complexed ribosomes☆

Abstract

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