The young and the restless: Isolating the dynamic mammalian preribosomes.

Despite the advances in understanding the assembly of yeast preribosomes using affinity purification and structural analysis, studies on mammalian ribosome biogenesis have lagged behind. Using an unbiased method to purify native mammalian preribosomal complexes from the nucleus, Abetov et al. now uncover two types of premature ribonucleoprotein complexes that are nutrient- and mTOR-dependent. This purification scheme, combined with genome-editing techniques, could be exploited to untangle the complexities underlying human ribosome biogenesis and ribosomopathies.