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Mismatch Repair

Mismatch Repair

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One of the common DNA damages is the chemical alteration of single bases by alkylation, oxidation, or deamination. The altered bases cause mispairing and strand breakage during replication. This type of damage causes minimal change to the DNA double helix structure and can be repaired by the base excision repair (BER) pathways. BER corrects damaged DNA sequences by removing the damaged base and restoring the original base sequence using the complementary strand as a template.
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Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations can be characterized in a number of different ways: whether and how they alter the amino acid sequence of the protein, whether they occur over a small or large area of DNA, and whether they occur in somatic cells or germline cells.
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Base Excision Repair

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One of the common DNA damages is the chemical alteration of single bases by alkylation, oxidation, or deamination. The altered bases cause mispairing and strand breakage during replication. This type of damage causes minimal change to the DNA double helix structure and can be repaired by the base excision repair (BER) pathways. BER corrects damaged DNA sequences by removing the damaged base and restoring the original base sequence using the complementary strand as a template.
The first step of...

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Related Experiment Video

Updated: Jun 15, 2026

Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

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Published on: March 6, 2013

Microcystins with Modified Adda⁵-Residues from a Heterologous Microcystin Expression System.

Christopher O Miles^1,2, Pearse McCarron¹, Krista Thomas¹

¹Biotoxin Metrology, National Research Council Canada, Halifax, Nova Scotia B3H 3Z1, Canada.

|July 1, 2024

Summary

This summary is machine-generated.

Researchers discovered 15 new microcystin analogues in engineered bacteria, including variants with modified Adda moieties lacking a phenyl group. This finding reveals unexpected biosynthetic flexibility in microcystin production.

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Area of Science:

Biochemistry
Microbiology
Analytical Chemistry

Background:

Microcystins are toxic cyclic peptides produced by cyanobacteria.
The unusual Adda amino acid is a key component of microcystins.
The microcystin gene cluster from *Microcystis aeruginosa* PCC 7806 was expressed in *Escherichia coli*.

Purpose of the Study:

To identify and characterize microcystin analogues produced by engineered *E. coli*.
To investigate modifications in the Adda moiety of microcystins.
To understand the biosynthetic flexibility of microcystin production.

Main Methods:

Semi-targeted liquid chromatography with high-resolution tandem mass spectrometry (LC-HRMS/MS).
Thiol derivatization.
In-source fragmentation of microcystin standards.

Main Results:

15 additional microcystin analogues were identified, including linear variants and 12 with Adda moiety modifications.
Four variants lacked the phenyl group at the Adda terminus, a novel finding in cyanobacteria.
Fragmentation analysis elucidated the origin of key ions in Adda-containing microcystins, aiding detection of variants.

Conclusions:

The engineered *E. coli* strain produces a diverse range of microcystin analogues beyond those initially reported.
Modifications to the Adda moiety, including phenyl group absence, were identified.
The study highlights the biosynthetic flexibility of the microcystin synthase complex and suggests substrate availability influences product formation.