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Mutation frequency and spectrum resulting from a single abasic site in a single-stranded vector

C W Lawrence1, A Borden, S K Banerjee

  • 1Department of Biophysics, University of Rochester School of Medicine, NY 14642.

Nucleic Acids Research
|April 25, 1990
PubMed

Insights

DNA abasic sites are mutagenic, especially when cells are SOS-induced. Replication often involves nucleotide insertion opposite the lesion, with specific base preferences observed, highlighting DNA repair and mutagenesis mechanisms.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Abasic sites are common DNA lesions that can arise from spontaneous base loss.
  • These lesions pose a significant challenge to DNA replication fidelity.
  • The SOS response in bacteria is a DNA damage-inducible system that can influence mutagenesis.

Purpose of the Study:

  • To investigate the mutagenic properties of a single abasic site in DNA.
  • To determine the replication outcomes at abasic sites in both SOS-induced and uninduced bacterial cells.
  • To characterize the types of nucleotide insertions and omissions occurring opposite abasic sites.

Main Methods:

  • Transfection of single-stranded M13mp7 vectors containing a single abasic site into E. coli.
  • Comparison of vector replication in SOS-induced versus uninduced bacterial cells.
  • Sequencing of progeny phage to analyze replication events at and around the abasic site.

Main Results:

  • Replication of vectors with abasic sites was significantly higher (5-7%) in SOS-induced cells compared to uninduced cells (0.1-0.7%).
  • In SOS-induced cells, 93-96% of replicated phage involved nucleotide insertion opposite the abasic site; the rest involved nucleotide omission.
  • Nucleotide insertion patterns showed a strong preference for dAMP (54-80%) and dGMP (15-20%) at the abasic site.

Conclusions:

  • Abasic sites are mutagenic, with their mutagenicity greatly enhanced by the SOS response.
  • DNA polymerase predominantly inserts nucleotides opposite abasic sites, with a bias towards adenine and guanine.
  • Mutations are typically confined to the abasic site, though rare flanking mutations can occur.

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