Cryo-EM structure of 90 S small ribosomal subunit precursors in transition states

How ribosomes are made The formation of eukaryotic ribosomes is a complex process that starts with transcription of a large precursor RNA that assembles into a large 90S preribosome, which matures to finally give the 40S small subunit of the ribosome. Cheng et al. and Du et al. give insight into this process, using cryo–electron microscopy to look at intermediates along the pathway. Together, these studies reveal how a cast of molecular players act to coordinate the compositional and structural changes that transform the 90S preribosome into a pre-40S subunit. Science , this issue p. 1470 , p. 1477