λ-prophage Induction in Repair-deficient and Wild Type E. Coli Strains by γ-rays and Heavy Ions

Summary

λ-prophage induction in repair-deficient and wild-type E. coli strains by heavy ions and γ-rays has been investigated. The dose dependence of the fraction of induced cells has been measured and its initial slope (λ-induction potency) determined. The induction by γ-rays was found to be more efficient in a polA-repair-deficient strain; the value of λ-induction potency is zero in lexA⁻ and recA⁻ strains. The λ-induction potency increased with LET for wild-type cells but remained constant in the case of polA⁻ mutant cells. It is suggested that the DNA damage triggering the λ-prophage induction in the case of ionizing radiation could be a type of DNA single-strand break with complex structure which cannot be repaired by fast repair processes, and which requires a substantial level of energy deposition for induction in a DNA molecule.