Pervasive Transcription-coupled DNA repair in E. coli

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Nucleotide excision repair (NER) encompasses Global Genomic Repair (GGR) and Transcription-Coupled Repair (TCR).
• GGR and TCR were traditionally considered distinct sub-pathways of NER.
• The precise roles and interplay of GGR and TCR in bacterial DNA repair remain incompletely understood.

Purpose of the Study:

• To investigate the relationship between GGR and TCR in E. coli using a high-resolution DNA repair assay.
• To determine the necessity of active transcription for the repair of both DNA strands.
• To elucidate the role of the DNA translocase Mfd and transcriptional termination in TCR.

Main Methods:

• Utilized CPD-seq, a next-generation sequencing assay, to quantify cyclobutane pyrimidine dimer (CPD) lesions.
• Measured CPD lesion levels before, during, and after UV-induced genotoxic stress in E. coli.
• Analyzed DNA repair rates at single-nucleotide resolution to assess genomic recovery.

Main Results:

• Active transcription is essential for the repair of both the template strand (TS) and non-template strand (NTS).
• The majority of TCR occurs independently of the Mfd translocase.
• Repair of both DNA strands is enhanced by readthrough of Rho-dependent terminators.
• UV stress induces global antitermination, increasing TCR accessibility to diverse genomic regions.

Conclusions:

• GGR and TCR are not distinct sub-pathways but rather facets of a unified repair process.
• Transcription plays a critical role in the complete repair of the bacterial genome.
• The interplay between transcription, DNA repair, and stress response mechanisms is more complex than previously thought.