Preferential replication-dependent mutagenesis in the lagging DNA strand in Escherichia coli

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• DNA replication fidelity is crucial for genomic stability.
• Mutations can arise during DNA replication, impacting gene function.
• Plasmid replication provides a model system to study mutagenesis.

Purpose of the Study:

• To investigate the influence of gene orientation relative to replication direction on mutation frequencies.
• To determine if DNA replication itself can be a source of specific mutations.
• To explore the role of the lagging strand in replication-dependent mutagenesis.

Main Methods:

• Utilized reporter genes for chloramphenicol (Cm) and tetracycline (Tc) resistance on a plasmid.
• Manipulated gene orientation relative to unidirectional ColE1-type replication.
• Induction of a dnaQ49 mutator strain to increase mutation rates.
• Monitored mutation frequencies over several DNA replication cycles.

Main Results:

• Mutation frequencies varied significantly based on reporter gene orientation.
• Higher mutation rates were observed when the reporter gene was in the same orientation as replication (lagging strand template).
• This orientation-dependent difference was transient, disappearing after mutations fixed in both DNA strands.

Conclusions:

• Replication direction and strand bias play a role in mutagenesis.
• The lagging strand appears to be preferentially targeted for replication-dependent mutations.
• Understanding these mechanisms is vital for fields ranging from cancer research to antibiotic resistance.