Mutation frequency decline in Escherichia coli. II. Kinetics support the involvement of transcription-coupled excision repair.
Mutation frequency decline (MFD) in Escherichia coli was examined to demonstrate repair of targeting photoproducts during the post-UV incubation required in this process. Repair of mutation-targeting cyclobutane pyrimidine dimers (T < > C) was demonstrated when a correlation was established between the mutation frequency normally associated with these lesions and the rate of mutation production at these lesions by spontaneous deamination of cytosines and photoreversal in ung-defective cells. An incubation producing a decline in mutation frequency, i.e., MFD, also produces lower rates of mutation increase via the deamination mechanism. Since the latter assay involves processes entirely within the post-UV incubation period, the lower rates are attributed to rapid transcription-coupled nucleotide excision repair (TCR) that reduces the number of relevant T < > C dimers during this period. Rediscovery of the neglected fact that MFD can be stimulated by post-UV incubation in buffer alone is part of the analysis. Results presented here and a variety of others are discussed to support a model of MFD as a particular example of TCR: effective repair of photoproducts in the transcribed DNA strand that target glutamine tRNA suppressor mutations occurs during the appropriate post-UV incubation and is responsible for MFD.
Bockrath
R
R
Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis 46202-5120, USA.
Li
B H
BH
D019297:2,4-Dinitrophenol; D004260:DNA Repair; D004140:Dinitrophenols / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D005947:Glucose / Q000494:pharmacology; D008027:Light; D008957:Models, Genetic; D016296:Mutagenesis; D011740:Pyrimidine Dimers / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics; D013489:Suppression, Genetic; D014158:Transcription, Genetic; D014466:Ultraviolet Rays / Q000009:adverse effects
D004140:Dinitrophenols; D011740:Pyrimidine Dimers; D012343:RNA, Transfer; D005947:Glucose; D019297:2,4-Dinitrophenol