# HELICASE ACTIVITY AND ITS ROLE IN TELOMERE AND TELOMERASE REGULATION

> **NIH NIH R01** · WASHINGTON UNIVERSITY · 2020 · $305,000

## Abstract

In this proposal we focus on the Pif1 sub-family of DNA helicases and test the hypothesis
that one of their functions is to facilitate DNA replication across naturally occurring barriers. We
showed that DNA-bound Rap1 is a barrier to the strand-displacement DNA synthesis activity of
DNA polymerase  and that Pif1 displaces Rap1, allowing DNA replication across the barrier.
We hypothesize that proteins bound to the DNA, at telomeres and non-telomeric sites, are
displaced by Pif1 to facilitate DNA replication, and that this activity is fundamental and
conserved among Pif1 homologues. G-quadruplexes and DNA hairpins can also be obstacles to
DNA replication. Pif1 is thought to facilitate replication-fork progression by unwinding G-
quadruplexes. However, little is known about this activity of Pif1 in the presence of single-
stranded DNA binding proteins (SSBs). We hypothesize that the activity of Pif1 is needed to
facilitate DNA replication across G-quadruplexes when SSBs cannot effectively melt the DNA
secondary structure. Furthermore, we hypothesize that Pif1 stimulates DNA synthesis by DNA
polymerase  across DNA hairpins.
 We showed that unwinding of dsDNA by a Pif1 monomer is balanced by a Pif1-dependent
DNA rewinding activity. We hypothesize that under physiological conditions rewinding is
inhibited by concomitant synthesis of DNA by polymerases. Mutations of Pif1 that affect the
balance between unwinding and rewinding will allow us to determine the origin of this newly
discovered property.
 To test these hypotheses, we propose three Aims: 1) determine whether protein obstacles
that impede DNA replication are displaced by Pif1; 2) determine whether DNA secondary
structures are unwound by Pif1 to facilitate DNA replication; 3) determine the mechanism
underlying the Pif1-dependent DNA rewinding activity.

## Key facts

- **NIH application ID:** 9884773
- **Project number:** 5R01GM098509-09
- **Recipient organization:** WASHINGTON UNIVERSITY
- **Principal Investigator:** Roberto Galletto
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $305,000
- **Award type:** 5
- **Project period:** 2011-08-01 → 2022-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9884773

## Citation

> US National Institutes of Health, RePORTER application 9884773, HELICASE ACTIVITY AND ITS ROLE IN TELOMERE AND TELOMERASE REGULATION (5R01GM098509-09). Retrieved via AI Analytics 2026-07-01 from https://api.ai-analytics.org/grant/nih/9884773. Licensed CC0.

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