# Uncovering mechanisms of rRNA flux through the nucleolus

> **NIH NIH F32** · WASHINGTON UNIVERSITY · 2024 · $76,756

## Abstract

PROJECT SUMMARY / ABSTRACT
 Ribosome biogenesis occurs in the nucleolus, and disruptions to nucleolar proteins cause
ribosomopathies such as Treacher Collins syndrome and contribute to a range of proliferative and degenerative
diseases. Nucleoli contain three nested sub-compartments that are phase-separated from each other and differ
in composition, density, and function. The inner-most fibrillar centers (FCs) are surrounded by dense fibrillar
components (DFCs). Transcription of ribosomal RNA (rRNA) occurs at the interface between the FC and DFC,
and maturation of rRNA occurs in the DFC. In the outermost phase, the granular component (GC), rRNA
incorporates ribosomal proteins to create ribosomal subunits. The equilibrium nature of phase separation implies
that the relevant factors concentrate themselves into specific phases without energy input. This coupled with the
nested architecture of the nucleolus, sets up thermodynamically controlled fluxes across the distinct layers.
Recent studies have described a molecular handoff model for setting up the inward flux of ribosomal proteins
into the granular component. However, ribosomal assembly requires an outward flux of rRNA, and how this is
set up, whether this is under thermodynamic control, and the key molecular players that set up such a flux remain
entirely unknown. My goal is to uncover the mechanisms that set up the flux of rRNA into and through the
granular component of the nucleolus.
 In my preliminary work I determined the critical factors involved in setting up rRNA flux and began
reconstituting this process in vitro. I used bioinformatics analysis and in vivo localization studies to identify the
protein nucleolin as the key protein that sets up rRNA flux. My reconstitutions show that nucleolin mediates rRNA
flux out of the DFC and into the GC. Recent studies in the literature and my preliminary studies show that
nucleolin helps set up the flux of rRNA through the GC. My preliminary data leads to the hypothesis that
ribosome biogenesis relies on the thermodynamic flux of rRNA into and through the granular component
(GC) and that this is primarily mediated by nucleolin. This hypothesis will drive my specific aims: 1 -
Determine which biophysical features of nucleolin (NCL) and rRNA complexes are required to set up
rRNA fluxes from the dense fibrillar component (DFC) into the granular component (GC) and 2 - measure
a series of linked phase equilibria of nucleolin, nucleophosmin, rRNA, and rProtein to determine if they
contribute to rRNA flux through the granular component

## Key facts

- **NIH application ID:** 11001388
- **Project number:** 3F32GM146418-01A1S1
- **Recipient organization:** WASHINGTON UNIVERSITY
- **Principal Investigator:** Matthew R King
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $76,756
- **Award type:** 3
- **Project period:** 2022-12-01 → 2024-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/11001388

## Citation

> US National Institutes of Health, RePORTER application 11001388, Uncovering mechanisms of rRNA flux through the nucleolus (3F32GM146418-01A1S1). Retrieved via AI Analytics 2026-05-28 from https://api.ai-analytics.org/grant/nih/11001388. Licensed CC0.

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