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DNA Helicases

DNA Helicases

DNA unwinding helicase enzymes are a type of motor protein. Motor proteins can translocate along filaments or polymers using energy generated from ATP hydrolysis. Helicases are involved in all the important cellular processes where DNA unwinding is required, such as DNA replication, repair, recombination, and transcription. They are present in all living organisms, but vary in their structure, function, and mechanism of action. For example, in prokaryotes, DnaB helicase binds and translocates...

Single-Strand DNA Binding Proteins

Single-Strand DNA Binding Proteins

For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...

DNA Topoisomerases

DNA Topoisomerases

Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. ...

Homologous Recombination

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...

Fixing Double-strand Breaks

Fixing Double-strand Breaks

The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...

Fixing Double-strand Breaks

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Related Experiment Video

Updated: Mar 25, 2026

Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes

Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes

Published on: April 4, 2025

G-quadruplexes and helicases.

Oscar Mendoza¹, Anne Bourdoncle¹, Jean-Baptiste Boulé²

¹University of Bordeaux, ARNA Laboratory F-33000 Bordeaux, France INSERM U1212,CNRS UMR 5320, IECB, F-33600 Pessac, France.

Nucleic Acids Research

|February 18, 2016

Summary

Guanine-rich DNA can form stable G-quadruplex structures. Helicase enzymes are increasingly studied for their ability to unfold these structures, potentially impacting genomic DNA.

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Area of Science:

Molecular Biology
Genetics
Biochemistry

Background:

Guanine-rich DNA sequences can fold into stable G-quadruplex structures in vitro.
These G-quadruplex structures are hypothesized to function as genomic DNA knots.
Proteins may have evolved to resolve these structures in vivo.

Purpose of the Study:

To provide a comprehensive overview of the field studying helicase enzymes and G-quadruplex DNA structures.
To summarize the current understanding of enzymatic G-quadruplex unfolding.

Main Methods:

Review of existing scientific literature on helicase enzymes and G-quadruplex DNA.
Analysis of studies reporting in vitro resolution of G-quadruplexes by helicases.

Main Results:

Since the late 1990s, numerous studies have demonstrated that various helicase enzymes can unfold G-quadruplex structures in vitro.
The number of reported studies in this area has significantly increased over time.

Conclusions:

Helicase enzymes are capable of resolving G-quadruplex DNA structures.
The enzymatic unfolding of G-quadruplexes by helicases is a growing area of research with potential implications for genome stability.