# Biophysical interrogation of the RNA-mediated mechanisms regulating Polycomb Repressive Complex 2 activity

> **NIH NIH F32** · UNIVERSITY OF COLORADO · 2022 · $67,174

## Abstract

PROJECT SUMMARY
 Polycomb repressive complex 2 (PRC2) is a histone methyltransferase (HMTase) that sequentially deposits three
methyl groups onto lysine 27 of histone H3 (H3K27me1/2/3), and its activity is crucial for epigenetic silencing during
development and cancer. How PRC2 is targeted to genetic loci is of considerable interest, given its critical function and
abundance of target genes. It’s well accepted that PRC2 interacts broadly with RNA, and that these interactions regulate
PRC2’s localization at genomic sites destined for epigenetic silencing. However, the details about the nature and
mechanism(s) of PRC2’s regulation by RNA remain quite controversial. While some studies have proposed a role for
RNA in PRC2’s recruitment to chromatin, more have suggested roles in PRC2 eviction from chromatin and/or inhibition
of PRC2 activity. Notably, a recent work has demonstrated that the PRC2-RNA interaction is critical in vivo for
maintaining H3K27me3 levels and chromatin occupancy at PRC2 target genes. Thus, while there’s evidence RNA plays a
role in evicting PRC2 from chromatin under certain conditions, it also seems it must facilitate chromatin binding and
H3K27me3 deposition in at least some circumstances. To date, the PRC2 literature lacks direct evidence for a mechanism
that can reconcile these prior data and explain RNA-mediated chromatin-binding and HMTase activity by PRC2. My
preliminary data unexpectedly imply PRC2 has the intrinsic capacity to transfer directly between polynucleotides, and this
phenomenon could be broadly relevant to RNA-mediated regulation of chromatin-modifying enzymes. Based on these
and other data, I hypothesize a ‘hand-off’ model where PRC2 can be directly transferred between nascent RNA and
spatially proximal chromatin to facilitate H3K27me3 deposition or eviction from chromatin. Studies proposed herein will
quantify PRC2’s binding and competition kinetics for RNA and DNA/nucleosomes, determine the polynucleotide species
PRC2 could be transferred between, characterize the prevalence and biophysical requisites of this phenomenon in other
proteins, and interrogate the effect of RNA-nucleosome spatial relationships on PRC2’s HMTase activity. Findings from
these studies will expand our understanding of how chromatin-modifying enzymes are regulated, which could have
profound implications in our understanding of cell differentiation, embryonic development, and cancer.

## Key facts

- **NIH application ID:** 10535223
- **Project number:** 1F32GM147934-01
- **Recipient organization:** UNIVERSITY OF COLORADO
- **Principal Investigator:** Wayne Oliver Hemphill
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $67,174
- **Award type:** 1
- **Project period:** 2022-09-01 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10535223

## Citation

> US National Institutes of Health, RePORTER application 10535223, Biophysical interrogation of the RNA-mediated mechanisms regulating Polycomb Repressive Complex 2 activity (1F32GM147934-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10535223. Licensed CC0.

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