Functions that Protect Escherichia coli from Tightly Bound DNA-Protein Complexes Created by Mutant EcoRII...

Area of Science:

• Bacteriology
• Molecular Biology
• Genetics

Background:

• Mutant EcoRII methyltransferase (M.EcoRII-C186A) forms tightly bound DNA-protein complexes (TBCs) on bacterial chromosomes.
• The mechanisms of lethality induced by these sporadic TBCs and their processing compared to covalent DNA-protein crosslinks (DPCs) are not well understood.

Purpose of the Study:

• To investigate the impact of M.EcoRII-C186A-induced TBCs on DNA replication forks in vivo.
• To identify cellular factors involved in protecting against TBCs and compare their roles with those protecting against DPCs.

Main Methods:

• 2D gel electrophoresis to detect replication fork stalling and TBC formation.
• Candidate gene screening to identify mutants hypersensitive to M.EcoRII-C186A-induced TBCs.
• Comparative analysis of mutant sensitivity to TBCs, DPCs, and quinolone antibiotics.

Main Results:

• M.EcoRII-C186A-induced TBCs were found to block replication forks, visualized as specific bubble molecules on 2D gels.
• Several proteins, including RecA, RecBC, RecG, RuvABC, UvrD, FtsK, XerCD, and SsrA, were identified as necessary for protection against TBCs.
• The RecFOR pathway and Rep helicase were specifically required for TBCs, but not for M.EcoRII-induced DPCs, suggesting distinct processing mechanisms.
• rep, ftsK, and xerCD mutants exhibited novel hypersensitivity to quinolone antibiotics.

Conclusions:

• Tightly bound, non-covalent protein complexes can stall replication forks, requiring specific cellular machinery for resolution.
• Distinct pathways, involving RecFOR and Rep helicase, are essential for processing TBCs, differing from DPC repair mechanisms.
• The study identifies novel roles for Rep, FtsK, and XerCD in DNA repair and highlights their involvement in quinolone-induced DNA damage.