Base substitution spectra of nalidixylate resistant mutations induced by monochromatic soft X and 60Co gamma-rays in Bacillus subtilis spores.
Bacillus subtilis spores were exposed to three types of photons, monochromatic soft X-rays with the energy corresponding to the absorption peak of phosphorus K-shell electron (2,153 eV) and with the slightly lower energy (2,147 eV), and 60Co gamma-rays. From the irradiated spores, 233 mutants exhibiting nalidixic acid resistance were isolated, and together with 94 spontaneous mutants, the sequence changes in the 5'-terminal region of the gyrA gene coding for DNA gyrase subunit A were determined. Among eighteen alleles of the gyrA mutations, eight were single-base substitutions, nine were tandem double-base substitutions, and one was a double substitution skipping a middle base pair. About 6% of the radiation-induced mutations were tandem double-base substitutions, whereas none was observed among the spontaneous ones. Among spontaneous mutations, A:T and G:C pairs were equally subjected to mutations, whereas the substitutions from G:C pairs and those to A:T pairs predominated among those induced with soft X-rays. The peak-energy X-rays were more effective in killing and causing mutations than the low-energy X-rays, however, there seemed no base-change events uniquely attributable to phosphorus K-shell absorption.
Takahashi
N
N
Biophysics Laboratory, Faculty of Science, Rikkyo (St. Paul's) University, Tokyo, Japan.
Hieda
K
K
Morohoshi
F
F
Munakata
N
N
D001412:Bacillus subtilis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects*; D020029:Base Pairing; D001483:Base Sequence; D003037:Cobalt Radioisotopes; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D004352:Drug Resistance, Microbial / Q000235:genetics; D005720:Gamma Rays; D005798:Genes, Bacterial; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D013171:Spores, Bacterial / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D014965:X-Rays
D003037:Cobalt Radioisotopes; D017931:DNA Primers; D004269:DNA, Bacterial; D009268:Nalidixic Acid