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An in vitro approach to identifying specificity determinants of mutagenesis mediated by DNA misalignments
1Department of Microbiology and Molecular Genetics, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark 07103.
Abstract:
In vitro, misalignments of the newly synthesized (primer) strand during DNA polymerization lead to deletion and/or complex frameshift mutations. In vivo, similar misalignments of repeated and quasipalindromic DNA sequences are predicted to be intermediates of mutagenesis. The mutagenic misalignments are mediated by complementary pairing between the sequence at the 3'-OH end of the newly synthesized DNA strand and sequences in the template or in the newly synthesized DNA. Mutant sequences are produced when the misaligned primers act as substrates for DNA polymerization. The misalignments responsible for detected mutant sequences were compared to similar misalignments that were not implicated in mutagenesis, and all misalignment possibilities were compared to the position of pausing during polymerization by Escherichia coli polymerase I or its Klenow fragment. These comparisons revealed three characteristics of in vitro misalignment specificity. First, the termini produced by pausing are likely to be precursors to mutagenic misalignments. Second, the absence of some potential misalignments from the detected spectrum is explained well by the predicted undetectability of the mutant sequences they produce. Third, factors distinct from pausing and mutant detectability are responsible for differences in the specificity of misalignment mutagenesis mediated by E. coli DNA polymerase I and Klenow polymerase during in vitro synthesis.
Insights
DNA polymerase misalignments during synthesis can cause frameshift mutations. Specific characteristics of these misalignments, including sequence features and polymerase type, influence mutation outcomes in vitro.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA polymerization involves synthesizing new DNA strands based on a template.
- Misalignments during this process can lead to errors, such as deletions and frameshift mutations.
- These errors are particularly relevant for repetitive and palindromic DNA sequences in vivo.
Purpose of the Study:
- To investigate the characteristics of DNA polymerase misalignments that lead to mutations in vitro.
- To compare mutagenic and non-mutagenic misalignments.
- To understand the role of DNA polymerase type and pausing in mutagenesis specificity.
Main Methods:
- In vitro DNA polymerization assays using Escherichia coli polymerase I and its Klenow fragment.
- Analysis of DNA sequences produced after polymerization to identify mutations.
- Comparison of misaligned primer termini with polymerase pausing sites and mutant sequence detectability.
Main Results:
- Misalignments at primer termini generated by polymerase pausing are likely precursors to mutations.
- Some potential misalignments do not result in detectable mutations because the resulting sequences are not easily identified.
- Factors beyond pausing and mutant detectability explain differences in mutagenesis specificity between E. coli DNA polymerase I and Klenow polymerase.
Conclusions:
- DNA polymerase misalignment specificity is influenced by primer termini, mutant sequence detectability, and polymerase-specific factors.
- Understanding these mechanisms is crucial for comprehending DNA repair and mutagenesis.
- The study provides insights into the fidelity of DNA replication and the origins of genetic variation.