Role of cellular systems in modifying the response to chemical mutagens

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Updated: Oct 2, 2026

A Standard Methodology to Examine On-site Mutagenicity As a Function of Point Mutation Repair Catalyzed by CRISPR/Cas9 and SsODN in Human Cells
10:07

A Standard Methodology to Examine On-site Mutagenicity As a Function of Point Mutation Repair Catalyzed by CRISPR/Cas9 and SsODN in Human Cells

Published on: August 25, 2017

B Strauss, K N Ayres, K Bose

    Basic Life Sciences
    |January 1, 1980
    PubMed

    Insights

    Neocarzinostatin and MNNG cause DNA damage, with survival depending on repair systems and other lethal lesions. MNNG induces mutations, particularly multiple linked ones, in E. coli, with rec A and uvr E strains showing altered mutation patterns.

    Area of Science:

    • Molecular Biology
    • Genetics
    • Biochemistry

    Background:

    • Neocarzinostatin (NCS) generates apurinic/apyrimidinic (AP) sites in DNA, repaired by the AP excision repair system.
    • Cell survival after NCS treatment is influenced by factors beyond AP site repair, suggesting other lethal DNA lesions.
    • MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) also induces multiple DNA lesions, which cells may process through various mechanisms.

    Purpose of the Study:

    • To investigate the DNA repair mechanisms and mutation induction following treatment with Neocarzinostatin (NCS) and MNNG.
    • To elucidate the role of specific repair pathways, such as the O6-methylguanine removal system and rec A/uvr E functions, in cellular response to MNNG.
    • To analyze the impact of DNA damage on DNA synthesis using in vitro systems with known nucleotide sequences.

    Main Methods:

    • Assessing cell survival and mutation frequency after exposure to NCS and MNNG in E. coli.
    • Investigating the induction of DNA repair systems, including the O6-methylguanine removal system, using chloramphenicol inhibition.
    • Utilizing a phi X174 DNA system to determine the precise nucleotide site where DNA polymerase I and AMV reverse transcriptase synthesis is blocked on damaged templates.

    Main Results:

    • MNNG treatment rapidly induces an O6-methylguanine removal system in E. coli, and its inhibition increases mutation frequency.
    • Induction of O6-methylguanine repair likely contributes to mutations occurring near DNA replication forks.
    • MNNG induces multiple, closely linked mutations, a phenomenon absent in rec A and uvr E mutant strains, which are also impaired in single-site mutation production.
    • DNA polymerase I synthesis is blocked one nucleotide before the damaged base on the template strand, while AMV reverse transcriptase can insert a base at the damaged site.

    Conclusions:

    • Cellular response to DNA damaging agents like NCS and MNNG involves complex repair pathways and the generation of various lesion types.
    • The O6-methylguanine repair system plays a significant role in modulating mutation frequency and location after MNNG exposure.
    • The rec A and uvr E genes are crucial for handling multiple, closely linked mutations induced by MNNG.
    • Different DNA polymerases exhibit distinct responses to damaged DNA templates, impacting replication fidelity and repair outcomes.

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