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Published on: March 25, 2020
RecA-independent single-stranded DNA oligonucleotide-mediated mutagenesis
Kenan C Murphy1, Martin G Marinus
1Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655, USA.
Bacteriophage lambda’s Beta protein enhances oligonucleotide-mediated mutagenesis in bacteria by protecting DNA from degradation. This single-stranded annealing protein (SSAP) facilitates genetic modifications like insertions, deletions, and substitutions.
Area of Science:
- Molecular Biology
- Microbial Genetics
- Bacteriophage Biology
Background:
- Oligonucleotide-mediated mutagenesis is a powerful tool for bacterial genetic engineering.
- The single-stranded annealing protein (SSAP) Beta from bacteriophage lambda significantly enhances this process in Escherichia coli.
- SSAP-independent mutagenesis occurs at lower frequencies but can be boosted by inhibiting host single-stranded DNA (ssDNA) exonucleases.
Purpose of the Study:
- To elucidate the mechanism by which bacteriophage lambda's Beta protein promotes high-frequency oligonucleotide-mediated mutagenesis.
- To understand the role of host ssDNA exonucleases in SSAP-dependent and SSAP-independent mutagenesis.
- To explore strategies for enhancing SSAP-independent mutagenesis.
Main Methods:
- Expression of bacteriophage lambda Beta protein in Escherichia coli.
- Induction of oligonucleotide-mediated mutagenesis using various mismatch repair (MMR) strategies (MMR-resistant mismatches, MMR-deficient hosts).
- Inactivation or inhibition of host ssDNA exonucleases in vivo.
Main Results:
- Expression of lambda Beta significantly increases the efficiency of oligonucleotide-mediated mutagenesis for chromosomal modifications.
- High mutagenesis rates are achievable using MMR-resistant mismatches or MMR-deficient hosts, allowing isolation of unselected mutations.
- Inhibition of ssDNA exonucleases enhances SSAP-independent mutagenesis, suggesting exonucleases degrade oligos.
Conclusions:
- Lambda Beta promotes high rates of oligo-mediated mutagenesis not only by annealing oligos to DNA but also by protecting them from host ssDNA exonuclease degradation.
- Host ssDNA exonucleases play a critical role in limiting SSAP-independent oligo-mediated mutagenesis.
- Targeting ssDNA exonucleases offers a potential strategy to improve SSAP-independent gene editing in bacteria.
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