The SPATA5-SPATA5L1-CINP-C1ORF109 complex is essential for cytoplasmic pre-60S ribosome maturation

The ribosome is a universally conserved and essential molecular machine. While the core process of ribosome biogenesis is conserved across eukaryotes, metazoans have evolved additional regulatory factors. Here, we performed a protein–protein interaction screen of endogenously affinity-tagged human ribosome biogenesis factors, which identified the eumetazoan-specific SPATA5–SPATA5L1–CINP–C1ORF109 (55LCC) complex as a key regulator of ribosome biogenesis. Cryo-EM and X-ray crystallography define the architecture of 55LCC, and acute depletion of individual components shows that all four are essential for cytoplasmic pre-60S maturation. Replacing endogenous components with mutant versions pinpoints critical functional interactions and reveals that the ATPase activity of SPATA5 is more important than that of SPATA5L1. These findings indicate that SPATA5 evolved from the solitary yeast ATPase Drg1 into the multiprotein 55LCC complex in metazoans and provide a foundation for further study of the role of 55LCC in pre-60S maturation. Proteomics interaction screen identifies SPATA5-SPATA5L1-CINP-C1ORF109 complex as an essential regulator of cytoplasmic pre-60S ribosome maturation in human cells.