title: Reversions of the two missense and one nonsense trp-mutations induced by UV-light or methyl methanesulfonate in E. coli wild type and its polAi and uvrE502 mutants.
abstract: Two missense mutations, trpA58 and trpA78, and one nonsense mutation-trp-ochre, were used to determine the types of base-pair substitution caused by ultra, violet irradiation and methyl methanesulfonate (MMS) in Escherichia coli. UV irradiation of the wild-type bacteria led to the formation of revertants mainly arising as a result of GC yields AT transitions (suppressor revertants of the trpA58 mutant). True revertants of the trp- mutant (arising via transitions of AT pairs) and 5-methyl tryptophan-sensitive (MT-s) Trp+ of the trpA78 mutant (arising via unidentified transversions) occurred at a lower frequency. The polAI mutation did not change the frequency of the UV-induced transitions GC yields AT or that of the substitutions of the AT pairs. The uvrE502 mutation significantly increased the frequency of the UV-induced revertants arising via the transition GC yields AT. Treatment of the wild-type bacteria with MMS resulted in the formation of revertants mainly due to the GC yields AT substitution, and with a lower frequency to the AT yields GC transitions. MMS also induced, with a low frequency, some transversions. The frequency of the MMS-induced GC yields AT transitions was enhanced in the uvrE502 mutant. On the other hand, the uvrE502 mutation eliminated or significantly lowered MMS-induced revertants arising as a result of AT yields GC transitions or transversions.
mesh_terms: D000227:Adenine Nucleotides; D001483:Base Sequence / Q000187:drug effects / Q000528:radiation effects; D001669:Biochemical Phenomena; D001671:Biochemistry; D003597:Cytosine Nucleotides; D004926:Escherichia coli / Q000187:drug effects / Q000528:radiation effects; D005796:Genes; D005815:Genetic Code; D006150:Guanine Nucleotides; D008698:Mesylates / Q000494:pharmacology*; D008741:Methyl Methanesulfonate / Q000494:pharmacology*; D009153:Mutagens; D009154:Mutation / Q000187:drug effects / Q000528:radiation effects; D010443:Peptide Chain Termination, Translational; D011831:Radiation Genetics; D013489:Suppression, Genetic / Q000187:drug effects / Q000528:radiation effects; D013942:Thymine Nucleotides; D014466:Ultraviolet Rays
chemical_list: D000227:Adenine Nucleotides; D003597:Cytosine Nucleotides; D006150:Guanine Nucleotides; D008698:Mesylates; D009153:Mutagens; D013942:Thymine Nucleotides; D008741:Methyl Methanesulfonate