Alan Tartakoff1, Patrick DiMario2, Eduard Hurt3, Brian McStay4, Vikram Govind Panse5 and David Tollervey6 1Case Western Reserve University, Cleveland, Ohio 44106, USA; 2Louisiana State University, Baton Rouge, Louisiana 70803, USA; 3Universität Heidelberg, Biochemistry Center, Heidelberg, Baden Württemberg 69120, Germany; 4Centre for Chromosome Biology, Galway H91 TK33, Ireland; 5Institute of Medical Microbiology, University of Zurich, Zurich CH-8057, Switzerland; 6Wellcome Trust Centre for Cell Biology, Edinburgh EH9 3BF, United Kingdom Corresponding author: amt10case.edu Abstract

The nucleolus is best known for housing the highly ordered assembly line that produces ribosomal subunits. The >100 ribosome assembly factors in the nucleolus are thought to cycle between two states: an operative state (when integrated into subunit assembly intermediates) and a latent state (upon release from intermediates). Although it has become commonplace to refer to the nucleolus as “being a multilayered condensate,” and this may be accurate for latent factors, there is little reason to think that such assertions pertain to the operative state of assembly factors.