# Regulatory mechanisms of protein and RNA phase transitions

> **NIH NIH F32** · UNIV OF NORTH CAROLINA CHAPEL HILL · 2021 · $66,390

## Abstract

Project Summary. Compartmentalization of molecules into distinct volumes is essential for cellular life.
Biomolecular condensates, composed of liquid-like, phase-separated protein and RNA, are important centers
of compartmentalization in diverse contexts. Phase-separated structures also play central roles in pathological
aggregates that cause disease. Despite the critical importance of phase separation in physiology and
pathology, the regulatory mechanisms that govern when and where condensates form in cells are unknown.
Our group discovered that biomolecular phase transitions play essential physiological roles in a multinucleate
fungus (Zhang et al., Molecular Cell 2015; Langdon et al., Science 2018). Specifically, the RNA-binding protein
Whi3 forms distinct, functional droplets with different RNA transcripts that regulate either the nuclear cycle or
cell polarity. How do cells control assembly and patterning of different droplets in space and time? Recent
reports demonstrated that membrane surfaces provide a powerful platform for promoting protein phase
separation (Case et al., Science 2019; Huang et al., Science 2019). However, no studies have examined the
role of membranes in controlling RNA-based phase transitions. In my preliminary studies, I found that Whi3
droplets stably associate with endomembranes in live cells. Moreover, I found that membranes promote phase
separation of Whi3 in vitro at substantially lower concentration compared to free-diffusing protein in solution.
These findings suggest that endomembrane surfaces regulate Whi3/RNA phase separation in space and time.
Intriguingly, I also found that Whi3 partitions strongly to interfaces between contacting membranes, suggesting
that regions of membrane contact between organelles or with the plasma membrane may regulate Whi3/RNA
phase separation. How is Whi3 recruited to endomembranes? My preliminary findings reveal that an
endomembrane-associated molecular chaperone component binds to Whi3 and tunes droplet properties.
Importantly, molecular chaperones are known to influence droplet behavior, potentially defining the emergent
identities and functions of droplets. Taken together, my findings suggest that (i) endomembranes promote and
regulate protein/RNA phase transitions and (ii) membrane-associated chaperones control droplet properties to
determine overall function. The objective of my proposed work is to elucidate the role of membranes and
associated chaperones in regulating and patterning phase separation in space and time. The first specific aim
will examine how membrane surfaces and interfaces control assembly of biomolecular condensates. The
second specific aim will evaluate how membrane-associated chaperones regulate the emergent properties and
functions of biomolecular condensates. This work will create innovative biophysical tools for the study of
protein/RNA phase transitions in vitro and in live cells. The overall outcome of this research will be a deeper
understanding of...

## Key facts

- **NIH application ID:** 10085995
- **Project number:** 5F32GM136055-02
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **Principal Investigator:** Wilton Thomas Snead
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $66,390
- **Award type:** 5
- **Project period:** 2020-01-06 → 2023-01-05

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10085995

## Citation

> US National Institutes of Health, RePORTER application 10085995, Regulatory mechanisms of protein and RNA phase transitions (5F32GM136055-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10085995. Licensed CC0.

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