Dependence of the broth effect and the phenomenon of mutation frequency decline on dose of the applied UV radiation was investigated in the strain Escherichia coli B/r Hcr+ thy trp. Reversions to Trp+ were followed. The degree of the broth effect and the mutation frequency decline is minimal within the range of UV doses corresponding to a survival of cells lower than 10(-1). In connection with the two effects, excision of thymine dimers, initiation of synthesis, synthesis and degradation of DNA were also investigated. It was found that stimulation or inhibition of an inaccurate postreplication repair mechanism, rather than inhibition or stimulation of excision of thymine dimers, are responsible for the broth effect and the mutation frequency decline, respectively.

• MeSH
• DNA, Bacterial biosynthesis   radiation effects   MeSH
• Escherichia coli metabolism   radiation effects   MeSH
• Culture Media * MeSH
• Mutation * MeSH
• DNA Repair MeSH
• Stereoisomerism MeSH
• Thymidine metabolism   MeSH
• Tryptophan biosynthesis   metabolism   MeSH
• Ultraviolet Rays * MeSH
• Dose-Response Relationship, Radiation MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA, Bacterial MeSH
• Culture Media * MeSH
• Thymidine MeSH
• Tryptophan MeSH

Both the post-replication and the excision repair mechanism participate in the induction of Trp+ revertants in Escherichia coli B/r Hcr+ thy trp after a UV-irradiation. At low radiation doses (surviving cell fraction greater than 10(-1) most Trp+ reversions are due to post-replication repair mechanism while at high doses (surviving cell fraction less than 10(-1)) the Trp+ reversions arise probably as the result of an inaccurate excision repair. The absolute accuracy of repair processes decreases with increasing radiation dose.

• MeSH
• DNA, Bacterial analysis   metabolism   radiation effects   MeSH
• Escherichia coli analysis   metabolism   radiation effects   MeSH
• Mutation MeSH
• DNA Repair * MeSH
• Radiation Effects MeSH
• Thymine analysis   MeSH
• Tryptophan biosynthesis   MeSH
• Ultraviolet Rays * MeSH
• Dose-Response Relationship, Radiation MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA, Bacterial MeSH
• Thymine MeSH
• Tryptophan MeSH

• MeSH
• Agar MeSH
• Arginine metabolism   MeSH
• Bacteriological Techniques MeSH
• Bacteriolysis MeSH
• Cell Division MeSH
• Time Factors MeSH
• DNA, Bacterial biosynthesis   MeSH
• Escherichia coli drug effects   growth & development   metabolism   MeSH
• Caffeine pharmacology   MeSH
• Colorimetry MeSH
• Culture Media MeSH
• Genetics, Microbial MeSH
• DNA Replication MeSH
• Thymine metabolism   MeSH
• Tritium MeSH
• Uracil metabolism   MeSH
• Cell Survival MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Agar MeSH
• Arginine MeSH
• DNA, Bacterial MeSH
• Caffeine MeSH
• Culture Media MeSH
• Thymine MeSH
• Tritium MeSH
• Uracil MeSH