Genome-wide RNAi Screening Identifies Protein Modules Required for 40S Subunit Synthesis in Human Cells

• Genome-wide RNAi screening identifies ∼300 factors required for 40S subunit production
• The E3 ubiquitin ligase CRL4 is required for nucleolar steps of ribosome maturation
• Intracellular Gln synthesis supports efficient nuclear maturation of 40S subunits

SummaryRibosome biogenesis is a highly complex process requiring many assisting factors. Studies in yeast have yielded comprehensive knowledge of the cellular machinery involved in this process. However, many aspects of ribosome synthesis are different in higher eukaryotes, and the global set of mammalian ribosome biogenesis factors remains unexplored. We used an imaging-based, genome-wide RNAi screen to find human proteins involved in 40S ribosomal subunit biogenesis. Our analysis identified ∼300 factors, many part of essential protein modules such as the small subunit (SSU) processome, the eIF3 and chaperonin complexes, and the ubiquitin-proteasome system. We demonstrate a role for the vertebrate-specific factor RBIS in ribosome synthesis, uncover a requirement for the CRL4 E3 ubiquitin ligase in nucleolar ribosome biogenesis, and reveal that intracellular glutamine synthesis supports 40S subunit production.

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