Visualizing Ribosome Biogenesis: Parallel Assembly Pathways for the 30S Subunit

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Science  29 Oct 2010:
Vol. 330, Issue 6004, pp. 673-677
DOI: 10.1126/science.1193220

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Ribosome Assembly Pathway

The bacterial ribosome is made up of two subunits (50S and 30S) that together comprise 55 proteins and three large ribosomal RNAs. Both subunits self-assemble from their components in vitro, and hence, Mulder et al. (p. 673) were able to use a derivation of time-resolved electron microscopy to monitor assembly of the 30S subunit. This approach identified 14 distinct assembly intermediates and allowed characterization of the population, conformation, and protein composition of the intermediates along the assembly pathway.


Ribosomes are self-assembling macromolecular machines that translate DNA into proteins, and an understanding of ribosome biogenesis is central to cellular physiology. Previous studies on the Escherichia coli 30S subunit suggest that ribosome assembly occurs via multiple parallel pathways rather than through a single rate-limiting step, but little mechanistic information is known about this process. Discovery single-particle profiling (DSP), an application of time-resolved electron microscopy, was used to obtain more than 1 million snapshots of assembling 30S subunits, identify and visualize the structures of 14 assembly intermediates, and monitor the population flux of these intermediates over time. DSP results were integrated with mass spectrometry data to construct the first ribosome-assembly mechanism that incorporates binding dependencies, rate constants, and structural characterization of populated intermediates.

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