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Proofreading

Proofreading

Synthesis of new DNA molecules starts when DNA polymerase links nucleotides together in a sequence that is complementary to the template DNA strand. DNA polymerase has a higher affinity for the correct base to ensure fidelity in DNA replication. The DNA polymerase furthermore proofreads during replication, using an exonuclease domain that cuts off incorrect nucleotides from the nascent DNA strand.Errors during Replication Are Corrected by the DNA Polymerase EnzymeGenomic DNA is synthesized in...

Mismatch Repair

Mismatch Repair

Mismatch Repair

Mismatch Repair

Translesion DNA Polymerases

Translesion DNA Polymerases

Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
TLS polymerases are found in all three domains of life - archaea, bacteria, and eukaryotes. Of the different classes of TLS polymerases, members of the Y family are fitted with specialized structures that...

Proofreading

Proofreading

Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template DNA strand. DNA polymerase has a higher affinity to add the correct base and ensures fidelity during DNA replication. Furthermore, it exhibits proofreading activity during replication, using an exonuclease domain that cuts off incorrect nucleotides from the nascent DNA strand.
Errors During Replication are Corrected by the DNA Polymerase Enzyme

Mismatch Repair

Mismatch Repair

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.
The Mutator Protein Family Plays a Key Role in DNA Mismatch Repair
The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic...

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Related Experiment Video

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DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis

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Evidence that errors made by DNA polymerase alpha are corrected by DNA polymerase delta.

Y I Pavlov¹, C Frahm, S A Nick McElhinny

¹Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA.

Current Biology : CB

|January 25, 2006

Summary

Yeast polymerase alpha with reduced fidelity causes mutations. Inactivating the proofreading function of polymerase delta, but not epsilon, significantly worsens this mutator effect, suggesting delta proofreads alpha errors.

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Proofreading and DNA Repair Assay Using Single Nucleotide Extension and MALDI-TOF Mass Spectrometry Analysis

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Area of Science:

Molecular Biology
Genetics
Biochemistry

Background:

Eukaryotic DNA replication initiates with RNA primers synthesized by polymerase alpha (pol α), which lacks proofreading.
Polymerase switch to proofreading-proficient polymerases delta (pol δ) and epsilon (pol ε) is crucial for accurate DNA synthesis.
The precise roles of pol δ and pol ε in replication remain incompletely understood.

Purpose of the Study:

To investigate the roles of pol δ and pol ε in maintaining genome stability during DNA replication.
To determine if pol δ or pol ε proofreads errors introduced by pol α during replication initiation.

Main Methods:

Utilized a yeast strain expressing a mutant pol α (pol1-L868M) with reduced fidelity in vitro and in vivo.
Assessed the mutator phenotype of the pol1-L868M strain under conditions of inactivated pol δ or pol ε 3' exonuclease activity.
Analyzed DNA polymerase activity, processivity, and fidelity using biochemical assays.

Main Results:

The yeast pol α mutant (L868M) exhibited normal catalytic activity and processivity but reduced fidelity in vitro.
In vivo, the pol1-L868M allele conferred a significant mutator phenotype.
This mutator phenotype was dramatically enhanced by the inactivation of pol δ's 3' exonuclease, but not pol ε's.

Conclusions:

The 3' exonuclease of pol δ likely functions in proofreading errors made by pol α during the initiation of Okazaki fragments on the lagging strand.
Intermolecular proofreading, where one polymerase corrects errors of another, may be a critical mechanism for genome stability.
This finding has implications for understanding various DNA transactions and maintaining genome integrity in eukaryotes.