# RPA and RPA-like Complexes at Telomeres

> **NIH NIH R01** · UNIVERSITY OF COLORADO · 2021 · $302,738

## Abstract

Project Summary/Abstract
Telomeres are specialized nucleoprotein structures at the ends of eukaryotic chromosomes that are required
for chromosome stability and cellular proliferation. These structures are essential for human health because
dysregulation of either telomere protection or telomerase activity causes many inherited and acquired human
diseases, with telomere dysfunction also closely tied to cancer and aging. Chromosomal ends consist of
tandem repeats of TG-rich sequences that terminate in a highly conserved 3¢ single-stranded DNA (ssDNA)
overhang. Management of this single-stranded overhang is one of the most critical aspects of telomere
maintenance. When left unprotected, this overhang initiates DNA damage responses, leading to catastrophic
events that permanently damage the genome and result in apoptosis or senescence. Recent data point to the
intricate integration of the general DNA-maintenance and telomere machineries. Understanding the interplay of
the genomic and telomere-specific ssDNA-binding factors is key to understanding the basic biology of
chromosome maintenance and the catastrophic consequences of its misregulation.
This program is focused on two protein complexes that manage ssDNA in many chromosomal contexts,
including at telomeres and replication forks. Human CTC1/STN1/TEN1(hCST) is a heterotrimeric protein
complex that protects and maintains sites of G-rich ssDNA throughout the genome. It acts prominently at
telomeres, binding the conserved G-rich overhang to coordinate the termination of telomerase activity and
recruitment of C-strand fill in by DNA pola-primase. Mutants of hCST are associated with a range of human
diseases characteristic of proliferation defects. As a first step in understanding the mechanism of action of
hCST, we have solved the high-resolution structure of hCST bound to ssDNA using cryoEM. This structure
provides surprising insights into hCST function and is an excellent starting point to address key mechanistic
questions regarding its function, such as its interaction with ssDNA, addressed in Aim 1, and the importance of
the decamer structure in cells, investigated in Aim 2. Our structure reveals that hCST most strikingly
resembles replication protein A (RPA), also a heterotrimeric complex involved in the non-specific binding of
ssDNA during replication, repair and recombination. The driving hypothesis for Aim 3 is based on the
observations that, in the context of certain mutants, RPA and CST activities can substitute for one another.
This leads to the testable hypothesis that these RPA mutants reveal a cryptic G-specific binding activity
contained within the protein. The structural, functional and biochemical parallels between the CST and RPA
complexes suggest a highly tuned interplay of their activities that allow for their crosstalk in the management of
difficult G-rich regions of chromatin, and this will be addressed in this aim.

## Key facts

- **NIH application ID:** 10212427
- **Project number:** 5R01GM139274-02
- **Recipient organization:** UNIVERSITY OF COLORADO
- **Principal Investigator:** DEBORAH S. WUTTKE
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $302,738
- **Award type:** 5
- **Project period:** 2020-07-07 → 2024-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10212427

## Citation

> US National Institutes of Health, RePORTER application 10212427, RPA and RPA-like Complexes at Telomeres (5R01GM139274-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10212427. Licensed CC0.

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