Features of Proteins That Allow Them to Form Nucleolar Compartments.

The nucleolus is an organelle which is responsible for ribosome biogenesis. Hundreds of proteins are involved in the process of ribosome biogenesis, and many of the proteins are concentrated by phase separation in the nucleolus. The nucleolus has three distinct compartments thought to be formed through phase separation, each with a specific role in ribosome biogenesis. The compartments include the fibrillar center (FC), dense fibrillar component (DFC), and the granular component (GC) which are responsible for rRNA synthesis, rRNA modification, and ribosome assembly respectively. We want to understand why proteins phase separate into certain compartments over another. To learn more about this phenomenon, we tested two hypotheses regarding nucleolar protein compartmentalization using Xenopus laevis oocytes. The first is that intrinsically disordered domains found in nucleolar proteins are sufficient to direct nucleolar domain compartmentalization. The second is that for some proteins, compartmentalization depends upon stable binding to multi-protein nucleolar complexes.