Inducible error-prone repair in Escherichia coli

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Ultraviolet (UV) radiation is a known mutagen, causing DNA damage that can lead to mutations.
• Postreplication repair (PRR) mechanisms are crucial for repairing DNA damage that escapes initial repair pathways.
• The precise mechanisms and genetic requirements for UV-induced mutagenesis and PRR are not fully understood.

Purpose of the Study:

• To test the hypothesis that UV-induced mutagenesis results from an error-prone PRR mode requiring the exrA+ recA+ genotype.
• To investigate the role of inducible repair products in UV mutagenesis and DNA repair.

Main Methods:

• Alkaline sucrose gradient centrifugation was used to assess DNA strand joining.
• Assays for mutation fixation, determined by loss of photoreversibility, were employed.
• The effect of chloramphenicol, a protein synthesis inhibitor, on PRR and mutation fixation was examined in various E. coli strains.

Main Results:

• Chloramphenicol treatment before UV irradiation prevented mutation fixation and partially inhibited PRR in E. coli WP2s uvrA.
• Chloramphenicol did not inhibit strand joining in uvrA bacteria with post-irradiation growth, in nonmutable uvrA exrA bacteria, or in uvrA tif bacteria under specific conditions.
• These findings suggest that an inducible product plays a role in a portion of PRR and is responsible for induced mutagenesis.

Conclusions:

• An inducible product is involved in a fraction of postreplication repair.
• This inducible repair product is responsible for UV-induced mutagenesis.
• The exrA+ recA+ genotype is essential for this UV-induced mutagenesis pathway.