Nitrous acid induced damage in T7 DNA and phage

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• Nitrous acid is a known mutagen that can damage DNA.
• Bacteriophage T7 is a well-characterized model organism for DNA repair studies.
• Previous research suggested certain DNA repair enzymes are vital for phage survival after mutagenic treatment.

Purpose of the Study:

• To investigate the effect of nitrous acid on T7 phage survival.
• To determine the role of specific DNA repair enzymes in repairing nitrous acid-induced DNA damage in T7 phage.
• To clarify discrepancies with previous reports regarding SOS response and repair mechanisms.

Main Methods:

• Exposure of T7 phage to nitrous acid (56 mM, pH 4.6) for varying durations.
• Assessing phage survival rates post-treatment.
• Comparing survival of wild-type and DNA repair-deficient Escherichia coli (E. coli) strains (lacking DNA polymerase I, exonuclease III, uvrA).
• Encapsulating treated DNA into empty phage heads to assess DNA-intrinsic damage.

Main Results:

• A 90% decrease in T7 phage survival occurred for every 10 minutes of nitrous acid exposure.
• Phage survival was similar whether nitrous acid treated DNA was in vivo or encapsulated.
• No increased survival was observed when growing SOS-induced wild-type E. coli.
• Nitrous acid treated phage survival was not reduced on E. coli deficient in DNA polymerase I, exonuclease III, or the uvrA component.

Conclusions:

• Specific DNA repair enzymes, including DNA polymerase I, exonuclease III, and the uvrA component of nucleotide excision-repair endonuclease, are not essential for repairing nitrous acid-induced damage in bacteriophage T7.
• The SOS response in E. coli does not enhance the survival of nitrous acid-treated T7 phage.
• Nitrous acid-induced DNA damage in T7 phage is repaired via mechanisms independent of these commonly studied bacterial repair pathways.