The Effects of Ionizing Radiation on Nucleic Acids of Bacteriophages and Bacterial Cells

Abstract

Electron spin resonance spectroscopy, radiation chemistry and radiation polymer chemistry contribute to the understanding of how the energy of ionizing radiations is distributed within the nucleic acid molecules and the number of kinds of chemical lesions that result from a given dose of the absorbed energy. Unlike the lesions induced the UV light and certain chemical agents, those induced by ionizing radiations are heterogeneous and usually remain unidentified. The 1:1 correspondence between one random energy absorption event ([image]60 eV) and biological inactivation of the single-stranded RNA and DNA molecules indicated that the radio-chemical lesions are of sufficient magnitude to derange the chemical specificity necessary for normal biological function. Such a simple correspondence does not exist for a double-stranded DNA molecules of bacteriophages. The reason for the lower killing efficiency may be only double-strand scissions are lethal, but an ionization event can effect such scissions only occasionally; some of the radiochemical lesions are repaired by the phage or the host-cell; and only a hit in a critical target occupying a small fraction of the genome can inactivate. Resolution of this question will be important for understanding such problems as phage replication, virus-host cell interaction and certain aspects of cancer research. The molecular and biological consequences of radiation damage inflicted upon the DNA of bacterial cell largely depends on the genetic constitution of this vital target. There are a number of parameters for a given strain of bacteria, which alter the yield of lesions per unit dose of radiation and their chance in ultimatley causing cell death. A major portion of the large variation in radiation sensitivity among different bacterial strains irradiated under a given set of conditions is the result of a variation in the efficiency of the gene-determined repair machinery. A wide variety of molecular aberrations induced in the bacterial DNA, by ionizing radiations and UV light and chemical agents are recognized and corrected in the cell.