sentence: This strategy , together with the CRISPR-Cas9-mediated GFP tagging of endogenous RBFs , has allowed us to identify distinct transitional pre-40S stages , clarify hitherto obscure roles of some RBFs , and uncover human-specific maturation events linked to the biosynthesis of the 40S ribosomal subunit.Previous proteomic and biochemical studies of preribosomes in yeast provided a wealth of information about ribosome maturation in that organism .