Ribosomal RNA Processing Shapes the Multiphase Nucleolus

Ribosome biogenesis takes place in the nucleolus, a three-layered liquid-like structure.

Discovery: The nucleolar architecture depends on correct ribosomal RNA processing.

Method: Spatiotemporal tracing of ribosomal RNA maturation through the nucleolar layers via

• 5eU pulse-chase and sequencing of ribosomal RNA processing steps

• imaging ribosomal RNA flux through the marked layers of the nucleolus

Synthetic nucleoli with altered structure can be formed from plasmid-encoded ribosomal RNA in mammalian cells.

This discovery demonstrates how non-equilibrium processes affect the self-assembly and morphology of multiphase condensates.