# Post-initiation control of conjugation by plasmid-encoded H-NS and NusG homologs

> **NIH NIH R21** · OHIO STATE UNIVERSITY · 2021 · $222,057

## Abstract

PROJECT SUMMARY
Many conjugative plasmids carry antibiotic-resistance genes and can transfer between distant
bacteria at high frequencies. Plasmids carrying colistin-resistance mcr alleles have been found
on five continents in agricultural, environmental, and clinical samples, and several of these also
carry extended-spectrum-lactamase and carbapenemase genes. This mobile resistome poses a
global threat to treatment of bacterial infections, but little is known about the regulation of plasmid
transfer that underlies this threat. Successful DNA transfer requires production and assembly of
many components of the conjugation machinery, which are organized into long 15-30 kb operons.
Expression of these operons, particularly in a heterologous host, imposes significant fitness costs;
genome-encoded H-NS and other nucleoid-associated proteins (NAPs) silence expression of
foreign genes and are required for maintenance of some plasmids. Silencing must be relieved for
conjugation to happen, and counter-silencers that interfere with H-NS binding to promoters and
enable transcription initiation have been described. However, the expression of long xenogeneic
operons is frequently silenced during elongation by the termination factor Rho, which acts in
concert with H-NS and the elongation factor NusG, and counter-silenced by operon-specific NusG
paralogs. Many conjugative plasmids encode H-NS and NusG homologs, which we propose
comprise an off/on switch of DNA transfer. We will use R6K, a model conjugative plasmid from
Escherichia coli, to test this idea; we already know that R6K-encoded H-NX inhibits conjugation.
In Aim 1, we will test the effects of cellular NAPs, NusG and Rho on silencing by H-NX, determine
its target sites, and investigate the mechanism of H-NX recruitment. In Aim 2, we will test whether
ActX, a NusG paralog encoded within the R6K transfer operon, activates conjugation and
promotes processive RNA synthesis. We hypothesize that H-NX/ActX pairs found on clinical
plasmids have co-evolved to assure successful dissemination of their resident plasmids, and
associated resistance determinants, through bacterial populations.

## Key facts

- **NIH application ID:** 10301108
- **Project number:** 1R21AI156441-01A1
- **Recipient organization:** OHIO STATE UNIVERSITY
- **Principal Investigator:** IRINA ARTSIMOVITCH
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $222,057
- **Award type:** 1
- **Project period:** 2021-06-09 → 2023-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10301108

## Citation

> US National Institutes of Health, RePORTER application 10301108, Post-initiation control of conjugation by plasmid-encoded H-NS and NusG homologs (1R21AI156441-01A1). Retrieved via AI Analytics 2026-05-29 from https://api.ai-analytics.org/grant/nih/10301108. Licensed CC0.

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