Major rearrangements in the 70S ribosomal 3D structure caused by a conformational switch in 16S ribosomal RNA.

Dynamic changes in secondary structure of the 16S rRNA during the decoding of mRNA are visualized by three-dimensional cryo-electron microscopy of the 70S ribosome, Thermodynamically unstable base pairing of the 912-910 (CUC) nucleotides of the 16S RNA with two adjacent complementary regions at nucleotides 885-887 (GGG) and 888-890 (GAG) was stabilized in either of the two states by point mutations at positions 912 (C912G) and 885 (G885U). A wave of rearrangements can be traced arising from the switch in the three base pairs and involving functionally important regions in both subunits of the ribosome, This significantly affects the topography of the A-site tRNA-binding region on the 30S subunit and thereby explains changes in tRNA affinity for the ribosome and fidelity of decoding mRNA.