Molecular biology: Protein binding cannot subdue a lively RNA

Abstract

Ribosomes, the cell’s protein-synthesis machines, are assembled from their components in a defined order. It emerges that the first assembly step must overcome dynamic structural rearrangements.

Figure 1. Binding of the S4 protein to an RNA five-way junction

a, Kim et al. studied a fragment of 16S ribosomal RNA, which consists of five duplex ‘arms’ radiating from a central junction, by attaching fluorescent probes to two of the arms. They observed that the RNA’s structure is highly dynamic, with the labelled arms (red) adopting a wide array of conformations. The other arms are also likely to move, but were not studied. b, The S4 protein forms a complex with 16S rRNA in the first step of ribosome assembly by binding to its preferred RNA conformation (binding step not shown). Once bound, S4 restrains, but does not fix, the movements of the RNA arms.