Replication restart: a pathway for (CTG).(CAG) repeat deletion in Escherichia coli

Area of Science:

• Molecular Biology
• Genetics
• DNA Replication and Repair

Background:

• (CTG)n.(CAG)n trinucleotide repeats are prone to high deletion rates in plasmids within Escherichia coli.
• DNA replication fork progression is frequently blocked during the synthesis of these repetitive sequences.

Purpose of the Study:

• To investigate the role of replication restart pathways in the high deletion rates of (CAG)n.(CTG)n repeats.
• To determine how mutations in replication restart genes affect trinucleotide repeat instability.

Main Methods:

• Measuring (CAG)n.(CTG)n deletion rates in various E. coli strains with mutations in replication restart genes.
• Analyzing mutational spectra in mutant strains.
• Investigating protein-DNA binding of PriA and RecG to repeat-containing DNA structures.

Main Results:

• Mutations in priA, recG, ruvAB, and recO significantly decreased repeat deletion rates.
• Mutations in priB and priC showed minor reductions in deletion rates.
• The recF mutation's effect on deletion rates was dependent on the template strand, while recJ slightly increased rates.
• PriA and RecG proteins exhibited binding to various DNA structures containing (CAG)n and/or (CTG)n loop-outs.

Conclusions:

• The high rates of trinucleotide repeat instability in E. coli are likely caused by the attempted restart of stalled replication forks at (CAG)n.(CTG)n repeats.
• Replication restart pathways, involving genes like priA and recG, play a crucial role in modulating trinucleotide repeat stability.