# Determinants of Coronavirus Fidelity in Replication and Pathogenesis

> **NIH NIH R01** · VANDERBILT UNIVERSITY MEDICAL CENTER · 2020 · $318,794

## Abstract

Summary: The SARS-CoV-2 pandemic (COVID-19) threatens the entire world’s health, economy and social
stability and is likely to continue for the foreseeable future. The capacity of this virus to cause protean
manifestations and resist public health control demonstrates its profound evolutionary and adaptive capacity.
We have studied the experimental evolution and determinants of fidelity and adaptation of CoVs for more than
20 years. The parent grant (R01 AI108197) for this proposed supplement defines the determinants of CoV
replicase proteins in virus fidelity and pathogenesis, and is specifically directed toward understanding the role of
the unique CoV exoribonuclease encoded in nonstructural protein 14 (nsp14-ExoN). Using SARS-CoV, MERS-
CoV and MHV, we have shown that nsp14-ExoN mediates RNA proofreading and is responsible for: i) CoV high
fidelity replication; ii) resistance to nucleoside analog inhibitors; iii) virus fitness; iv) evasion of host immunity;
and v) virulence in vivo. Engineered mutants of MHV and SARS-CoV lacking ExoN (ExoN(-)) are impaired in all
of the above functions and thus define ExoN as an exceptionally conserved and vulnerable virus encoded target
for inhibition and attenuation. In this administrative supplement, we propose in vitro and in vivo studies of SARS-
CoV-2 nsp14-ExoN, with the long-term goal define its role in virus replication and as a target for inhibitors and
attenuation. We will rescue SARS-CoV-2 mutants of nsp14-ExoN and define their impact on replication and
disease. In Aim 1, we will introduce mutations into SARS-CoV-2CoV-2 nsp14-ExoN that are known in SARS-
CoV, MERS-CoV, and/or MHV to abolish proofreading, alter nucleoside analog sensitivity, impact virus
replication and fitness, or decrease virulence. Recovered viruses will be tested for these phenotypes. In Aim 2,
we will select replication-competent ExoN mutants with defined phenotypes for testing in highly relevant human
airway epithelial (HAE) cultures and in a mouse model for SARS-CoV-2 replication and disease. The long-
standing and highly productive collaboration between the Denison and Baric labs has already resulted in
development of SARS-CoV-2 reverse genetics, initial analysis SARS-CoV-2 recombination, and potential animal
models, all of which, in combination with our established bioinformatics pipelines, will allow rapid progress on
the proposed supplement aims and will provide data for longer-term detailed studies of the role of ExoN and the
viral polymerase. The significance and urgency of these studies is high, as they will rapidly result in identification
of nsp14-ExoN targets for small molecule inhibitors and multiple pathways to stable and universal attenuation of
SARS-CoV-2 and future zoonotic CoVs.

## Key facts

- **NIH application ID:** 10167508
- **Project number:** 3R01AI108197-08S1
- **Recipient organization:** VANDERBILT UNIVERSITY MEDICAL CENTER
- **Principal Investigator:** Ralph S Baric
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $318,794
- **Award type:** 3
- **Project period:** 2020-07-06 → 2023-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10167508

## Citation

> US National Institutes of Health, RePORTER application 10167508, Determinants of Coronavirus Fidelity in Replication and Pathogenesis (3R01AI108197-08S1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10167508. Licensed CC0.

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