Deletions induced by gamma rays in the genome of Escherichia coli.
An Escherichia coli lysogen was constructed with a lambda phage bearing a lacZ gene surrounded by about 100 x 10(3) base-pairs of dispensable DNA. The lacZ mutants induced by gamma rays in this lysogen were more than 10% large deletions, ranging in size from 0.6 x 10(-3) to 70 x 10(3) base-pairs. These deletions were centered, not on lacZ, but on a ColE1 origin of DNA replication located 1.2 x 10(3) bases downstream from lacZ. This suggested that this origin of replication was involved in the process by which the deletions were formed. In agreement with this hypothesis, a lysogen of the same phage without the ColE1 origin showed a very much lower percentage of radiation-induced deletions, as did a second lysogen of a lambda phage without any known plasmid origin of replication. Indirect evidence is presented for radiation-induced deletions centered on the lambda origin of DNA replication in a lysogen. It is suggested that high percentages of large deletions may occur among radiation-induced mutations in mammalian cells because deletions centered on some of the thousands of origins of replication in these genomes do not kill the cells.
Raha
M
M
Department of Molecular Biophysics and Biochemistry Yale University, New Haven, CT 06511.
Hutchinson
F
F
D010582:Bacteriophage lambda / Q000235:genetics; D001483:Base Sequence; D002872:Chromosome Deletion; D004269:DNA, Bacterial / Q000235:genetics / Q000528:radiation effects; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects*; D005720:Gamma Rays; D005798:Genes, Bacterial / Q000528:radiation effects*; D008242:Lysogeny; D008969:Molecular Sequence Data; D015183:Restriction Mapping; D001616:beta-Galactosidase / Q000235:genetics / Q000528:radiation effects
D004269:DNA, Bacterial; D001616:beta-Galactosidase