# Determinants of Coronavirus Fidelity in Replication and Pathogenesis

> **NIH NIH R01** · VANDERBILT UNIVERSITY MEDICAL CENTER · 2021 · $447,335

## Abstract

PROJECT SUMMARY
Viruses in the Coronaviridae family (CoVs) have emerged as zoonoses with pandemic potential twice in the
21st century, causing severe human disease. Middle East respiratory syndrome (MERS)-CoV continues to
cause new cases of lethal respiratory infections with 35% mortality. Further, severe acute respiratory syndrome
(SARS)-like bat CoVs currently circulating are capable of infecting human cells, establishing the risk for future
emergence of zoonotic CoVs. There are no approved vaccines or antivirals for any human or zoonotic CoV,
emphasizing the importance of identifying vulnerable and broadly conserved CoV targets for therapeutic
intervention and vaccine development. Most RNA viruses generate genetic diversity required for interspecies
movement and adaptation via error-prone RNA-dependent RNA polymerases (RdRps) that lack proofreading.
In contrast, all CoVs encode a 3'-to-5' exoribonuclease (ExoN) in nonstructural protein 14 (nsp14-ExoN) that is
a key driver of CoV evolution and adaptation via RNA-dependent RNA proofreading. During the four years of
funding for this program, we have shown that CoV nsp14-ExoN mediates high-fidelity replication and that CoVs
lacking ExoN activity (ExoN(-)) are less fit during infection in cell culture, more sensitive to RNA mutagens, and
attenuated in a murine model of SARS-CoV infection. Our findings suggest that divergent β-CoVs - MERS-CoV,
SARS-CoV, and murine hepatitis virus (MHV) - have differential requirements for ExoN to sustain viability and
overall fitness. Finally, ExoN may play important and previously unpredicted functions in CoV resistance to
host innate immune surveillance. Thus, our published and preliminary studies support the scientific premise
that nsp14-ExoN is a master regulator of CoV fitness, evolution, and pathogenesis via functions in viral
replication, fidelity, and evasion of host innate immune responses. Specific aims of this proposal will define: 1)
Sequence and structural determinants of nsp14-ExoN-mediated functions in CoV replication, fidelity, and
interferon sensitivity; 2) Adaptations in nsp14, nsp12-RdRp, and elsewhere in the CoV replicase that
compensate for loss of ExoN-mediated fidelity; and 3) Mechanisms of ExoN regulation of the innate antiviral
immune response in vitro and in vivo. The availability of a high-resolution structure of nsp14; facile reverse
genetics systems for MHV, SARS-CoV, and MERS-CoV; and robust, relevant animal models for SARS-CoV
and MERS-CoV will allow us to address these questions, resulting in a comprehensive understanding of ExoN
roles and mechanisms in CoV replication, adaptation, and pathogenesis. These studies will catalyze
approaches targeting ExoN as a basis for stably attenuated CoV vaccines and novel antiviral drugs.

## Key facts

- **NIH application ID:** 10265802
- **Project number:** 3R01AI108197-09S1
- **Recipient organization:** VANDERBILT UNIVERSITY MEDICAL CENTER
- **Principal Investigator:** Ralph S Baric
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $447,335
- **Award type:** 3
- **Project period:** 2020-07-06 → 2023-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10265802

## Citation

> US National Institutes of Health, RePORTER application 10265802, Determinants of Coronavirus Fidelity in Replication and Pathogenesis (3R01AI108197-09S1). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10265802. Licensed CC0.

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