Kinetic Studies of the Effect of Restoration of a Required Amino Acid on Post-irradiation DNA Degradation and Cell Permeability

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Abstract
The kinetics of formation of the inducible inhibitor of post-irradiation DNA degradation has been studied by amino-acid deprivation in four Escherichia coli strains: 15T–(555–7), B/r59, WP2 and B32. In the first three, the inducible inhibitor is absent if the required amino acid is withheld and DNA degradation following gamma radiation is considerable. After restoration of the amino acid, the inhibitor appears in 7 min and is at 50 per cent maximum in 14 min. In B32 there is no effect of witholding the amino acid. Strain 555–7 also exhibits cell leakage, probably due to the induction of a defective prophage. This leakiness appears at 14 min with a 50 per cent maximum at 22 min. Strains WP2 and B/r59 have very little post-irradiation leakiness yet show strong induced inhibition. The data suggest that there is no necessary connection between the inducible inhibitor and a prophage. Preliminary U.V. induction in WP2 produces nearly complete inhibition, yet confers very little survival potential.