The homodimeric repressor of secondary metabolism (RsmA) binds to the ribosome-binding sites of a subset of bacterial mRNAs to repress translation, but in response to environmental stimuli, RsmA is sequestered by the binding of the small non-coding RNA (sRNA) RsmZ. Allain and colleagues now report the structural basis of RsmA sequestration by Pseudomonas fluorescens RsmZ. They show that RsmA binds to the GGA motifs of RsmZ and that RsmZ can bind up to five RsmA dimers in a sequential, ordered and cooperative manner. Two distinct ribonucleoprotein conformations were observed, which suggests that there are two assembly pathways. Finally, RsmZ contains three RNase E cleavage sites that are located close to the GGA motifs; thus, in addition to sequestering RsmA, progressive binding of RsmA protects the sRNA from degradation by RNase E.
References
Duss, O. et al. Structural basis of the non-coding RNA RsmZ acting as a protein sponge. Nature http://dx.doi.org/10.1038/nature13271 (2014)
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Du Toit, A. Bacterial small RNAs scoop up proteins. Nat Rev Microbiol 12, 460 (2014). https://doi.org/10.1038/nrmicro3293
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DOI: https://doi.org/10.1038/nrmicro3293