title: Gamma-radiation-induced mutation spectrum in the episomal lacI gene of Escherichia coli under oxic conditions.
abstract: In this study we have determined the mutation spectrum in the complete episomal lacI gene of Escherichia coli induced by gamma-radiation under oxic conditions. Mutants were generated by 60Co gamma-irradiation of an E. coli culture of stationary cells in LB medium, under continuous flushing with oxygen. Oligonucleotide probe analysis showed that 14% of the gamma-ray-induced mutations were located at the lacI gene hot spot at position 620-632, which is characterized by a triple repeat of the 5'-TGGC-3' sequence. Previously it was shown that about 70% of the spontaneous mutations were located at this site due to the loss or the addition of a TGGC sequence. The non-hot spot mutations were further characterized by automated sequence analysis. The results show that base pair (bp) substitutions were the main type of gamma-ray-induced mutations. Although all types of bp substitutions were observed, 74% of the bp substitutions involved C/G base pairs. C/G --> T/A and C/G --> A/T substitutions were predominant, both accounting for 35% of all bp substitutions, whereas A/T --> C/G substitutions were only seldomly observed (3%). A relatively large amount of -1 bp deletions (15% of all mutations) was detected in the gamma-ray-induced mutation spectrum, mainly affecting C/G base pairs, and 10% were deletions, ranging in size from 11 to 532 bp. It can be concluded that under oxic conditions gamma-radiation induces in E. coli mainly bp substitutions of all types but preferentially at C/G base pairs, and that the mutations tend to be randomly distributed within the lacI gene sequence.
authors.affiliation: Department of Medical Oncology, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands.
authors.forename: C A
authors.initials: CA
authors.lastname: Wijker
authors.forename: M V
authors.initials: MV
authors.lastname: Lafleur
authors.forename: H
authors.initials: H
authors.lastname: van Steeg
authors.forename: G R
authors.initials: GR
authors.lastname: Mohn
authors.forename: J
authors.initials: J
authors.lastname: Retèl
mesh_terms: D000332:Aerobiosis; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001482:Base Composition; D001483:Base Sequence; D003037:Cobalt Radioisotopes; D004252:DNA Mutational Analysis; D017931:DNA Primers; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects*; D029968:Escherichia coli Proteins; D016368:Frameshift Mutation; D005720:Gamma Rays; D005798:Genes, Bacterial / Q000528:radiation effects*; D056968:Lac Repressors; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D003037:Cobalt Radioisotopes; D017931:DNA Primers; D029968:Escherichia coli Proteins; D056968:Lac Repressors; C539064:LacI protein, E coli; D012097:Repressor Proteins