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Related Concept Videos

Types of RNA01:20

Types of RNA

Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs perform diverse functions and can be broadly classified as protein-coding or non-coding RNA. Non-coding RNAs play important roles in regulating gene expression in response to developmental and environmental changes. Non-coding RNAs in prokaryotes can be manipulated to develop more effective antibacterial drugs for human or animal use.
RNA Performs Diverse...
Types of RNA01:23

Types of RNA

Overview
Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs perform diverse functions and can be broadly classified as protein-coding or non-coding RNA. Non-coding RNAs play important roles in the regulation of gene expression in response to developmental and environmental changes. Non-coding RNAs in prokaryotes can be manipulated to develop more effective antibacterial drugs for human or animal use.
RNA...
RNA Stability01:53

RNA Stability

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations between RNA and DNA underlie the differences in their stability and longevity. Because DNA is double-stranded, it is inherently more stable. The single-stranded structure of RNA is less stable but also more flexible and can form weak internal bonds. Additionally, most RNAs in the cell are relatively short, while DNA can be up to 250 million...
RNA Stability01:53

RNA Stability

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations between RNA and DNA underlie the differences in their stability and longevity. Because DNA is double-stranded, it is inherently more stable. The single-stranded structure of RNA is less stable but also more flexible and can form weak internal bonds. Additionally, most RNAs in the cell are relatively short, while DNA can be up to 250 million...
Negative Regulator Molecules01:23

Negative Regulator Molecules

Positive regulators allow a cell to advance through cell cycle checkpoints. Negative regulators have an equally important role as they terminate a cell’s progression through the cell cycle—or pause it—until the cell meets specific criteria.
Bacterial Transcription01:53

Bacterial Transcription

RNA polymerase (RNAP) carries out DNA-dependent RNA synthesis in both bacteria and eukaryotes. Bacteria do not have a membrane-bound nucleus. So, transcription and translation occur simultaneously, on the same DNA template.
Transcription can be divided into three main stages, each involving distinct DNA sequences to guide the polymerase. These are:

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Related Experiment Video

Updated: Jul 1, 2026

Overexpressing and Purifying a Toxic Nuclease from Escherichia coli
08:13

Overexpressing and Purifying a Toxic Nuclease from Escherichia coli

Published on: August 29, 2025

Hypernegative supercoiling inhibits growth by causing RNA degradation.

Imad Baaklini1, Valentine Usongo, Flora Nolent

  • 1Département de Microbiologie et Immunologie, Université de Montréal, 2900 Edouard-Montpetit, Room R-612, Montréal, Québec H3C 3J7, Canada.

Journal of Bacteriology
|September 16, 2008
PubMed
Summary

Transcription-induced hypernegative supercoiling in Escherichia coli mutants causes growth arrest by facilitating RNA degradation. Overexpressing RNase HI alleviates this by limiting supercoiling and preventing RNA degradation.

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CD Spectroscopy to Study DNA-Protein Interactions
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Last Updated: Jul 1, 2026

Overexpressing and Purifying a Toxic Nuclease from Escherichia coli
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Overexpressing and Purifying a Toxic Nuclease from Escherichia coli

Published on: August 29, 2025

CD Spectroscopy to Study DNA-Protein Interactions
06:48

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Published on: February 10, 2022

Area of Science:

  • Molecular Biology
  • Genetics
  • Microbiology

Background:

  • Transcription-induced hypernegative supercoiling is characteristic of topoisomerase I (topA) mutants in Escherichia coli.
  • The physiological role of this supercoiling has been poorly understood.

Purpose of the Study:

  • To elucidate the physiological significance of transcription-induced hypernegative supercoiling in Escherichia coli.
  • To investigate the link between hypernegative supercoiling, mRNA processing, and bacterial growth.

Main Methods:

  • Utilized temperature downshift experiments on topA mutants.
  • Assessed effects of RNase HI overexpression on growth and supercoiling.
  • Analyzed mRNA levels, polysome abundance, and protein synthesis rates.
  • Conducted in vitro transcription assays to study R-loop formation.

Main Results:

  • Temperature downshift induced transient growth arrest and increased hypernegative supercoiling, exacerbated at lower temperatures.
  • RNase HI overexpression alleviated both growth arrest and hypernegative supercoiling.
  • Observed mRNA truncation, reduced polysomes, decreased protein synthesis, and altered mRNA processing during growth arrest.
  • In vitro transcription showed increased R-loop formation on hypernegatively supercoiled templates.

Conclusions:

  • Hypernegative supercoiling inhibits bacterial growth by promoting nascent RNA degradation.
  • RNase HI plays a protective role by limiting hypernegative supercoiling and subsequent RNA degradation.
  • A model is proposed where gyrase-induced hypernegative supercoiling facilitates RNA degradation, while RNase HI mitigates this effect.