EFFECTS OF PRIOR ALTERATION IN NUCLEIC ACID AND PROTEIN METABOLISM ON SUBSEQUENT MACROMOLECULAR SYNTHESIS BY IRRADIATED BACTERIA

Abstract

The extent and rate of deoxyribonucleic acid (DNA) synthesis is Escherichia coli is only partially inhibited by 10,000 r of X-rays with no apparent delay in the onset of synthesis. Interference with protein synthesis prior to irradiation of these cells increased the sensitivity of their DNA synthesizing system. Either chloramphenicol pretreatment or amino acid deficient growth with an auxotroph induced a delay in DNA synthesis when the treated cells were returned to a more equitable environment. Exposure of these pretreated cells to 10,000 r of X-rays greatly extended the lag in DNA synthesis upon subsequent reincubation in growth-supporting medium. These results suggest that the synthesis of a protein(s) constituent (ribonucleic acid cannot be ruled out) is a necessary part of the DNA replicating cycle and that X-ray exposure interferes with the formation of this component to a greater extent than it interferes with its function once formed.