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DNA Helicases

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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...

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The Replisome

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DNA replication is carried out by a large complex of proteins that act in a coordinated matter to achieve high-fidelity DNA replication. Together this complex is known as the DNA replication machinery or the replisome.
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In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
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Related Experiment Video

Updated: May 19, 2026

Hybrid Ensemble and Single-molecule Assay to Image the Motion of Fully Reconstituted CMG

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Published on: July 26, 2024

The eukaryotic Mcm2-7 replicative helicase.

Sriram Vijayraghavan¹, Anthony Schwacha

¹Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, 15260, USA.

Sub-Cellular Biochemistry

|August 25, 2012

Summary

The eukaryotic replicative helicase, Mcm2-7, uses a unique six-subunit structure with a regulated gate to unwind DNA. Accessory proteins like Cdc45 and GINS activate this gate for DNA replication during S-phase.

Area of Science:

Molecular Biology
Biochemistry
Structural Biology

Background:

The Mcm2-7 complex is the core of the eukaryotic replicative helicase, essential for DNA unwinding.
Unlike simpler helicases, Mcm2-7 is a hexamer composed of six distinct subunits.
Its toroidal structure superficially resembles prokaryotic and viral homohexameric helicases.

Purpose of the Study:

To elucidate the functional significance of the unique six-subunit assembly in the Mcm2-7 complex.
To understand the mechanism of Mcm2-7 activation and DNA unwinding.
To investigate the role of accessory proteins in regulating helicase activity.

Main Methods:

Biochemical analyses of the Mcm2-7 complex and the CMG complex.
Structural analyses of Mcm2-7 and associated activator proteins.

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Biochemical reconstitution of eukaryotic DNA replication.

Main Results:

Mcm2-7 possesses specific ATPase active sites for DNA unwinding, with one site forming a regulated gate.
Activation of Mcm2-7 during S-phase requires Cdc45 and GINS, which likely close the gate.
Mcm2-7 loads as a double hexamer at origins but does not function as a pump during elongation.

Conclusions:

The unique subunit composition of Mcm2-7 facilitates regulated DNA unwinding through a gate mechanism.
Accessory proteins are crucial for activating the Mcm2-7 helicase by modulating the gate.
Understanding Mcm2-7 function provides insights into eukaryotic DNA replication initiation and elongation.