LAMBDA-PROPHAGE INDUCTION IN REPAIR-DEFICIENT AND WILD-TYPE ESCHERICHIA-COLI STRAINS BY GAMMA-RAYS AND HEAVY-IONS

λprophage induction in repair-deficient and wild-type E. coli strains by heavy ions and γrays has been investigated. The dose dependence of the fraction of induced cells has been measured and its initial slope (λinduction potency) determined. The induction by γrays was found to be more efficient in a polA-repair-deficient strain; the value of λinduction potency is zero in lexA- and recA- strains. The λinduction 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 λprophage 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. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.