What is the role of the nucleolus in ribosome assembly?

[NatalieL]

I've been trying to understand the specific role of the nucleolus in ribosome assembly for my cell biology class, but I keep getting tangled up in the difference between the rRNA transcription and the actual assembly of the subunits. My textbook makes it seem like a straightforward assembly line, but I’ve read papers suggesting the process involves a lot more transient, intermediate structures.

[Daniel.W]

In the nucleolus, the 45S pre-rRNA is transcribed and initial processing starts; the construction of the subunit precursors is not a neat handoff but a swarm of transient assembly factors and intermediate particles.

[EricFJ]

I tried to track processing by pulse-chase and found several mid stages that only briefly accumulate before moving on.

[IsabellaYT]

I read papers showing U3 snoRNPs steer early cleavages and that many assembly factors must cycle on and off; if you knock one out, the process stalls at a specific precursor.

[MatthewDG]

I keep bumping into the same thing: it isn't a clean pipeline. Transcription, cleavage, and assembly seem to overlap, with many particles existing only briefly before maturing or being recycled.