title: A mutant of Eshcerchia coli K-12, URT-43, with a temperature-sensitive defect at the incision step  of the excision repair mechanism.
abstract: URT-43, which has a defect in excision repair, exhibits a temperature-dependent ultraviolet survival. It was shown that URT-43 requires protein synthesis but not DNA synthesis for recovery, by examining recovery in a growth medium containing chloramphenicol or nalidixic acid. The recovery of irradiated bacteriophage lambda in URT-43 took place in a medium containing nalidixic acid at 30 degrees, but not at 41 degrees, and chloramphenicol prevented this recovery. These results seem to imply that the product of the mutated gene in URT-43 is labile. URT-43 was confirmed to have a temperature-sensitive mutation at the incision step of the excision repair mechanism by examining the nick formation of parental DNA in alkaline sucrose gradients. The release of pyrimidine dimers was reinvestigated directly by one- and two-dimensional paper-chromatography and indirectly by examining the distribution of DNA molecules synthesized after irradiation. Dimers were excised into the acid-soluble fraction when growing bacteria were incubated, but were not excised when in amino acid starved bacteria. These results suggest that URT-43 is a mutant slowly excising pyrimidine dimers because the product of a mutated gene concerned with the incision step of the excision repair mechanism is unstable.
mesh_terms: D002501:Centrifugation, Zonal; D002701:Chloramphenicol / Q000494:pharmacology; D002854:Chromatography, Paper; D003090:Coliphages / Q000528:radiation effects; D004260:DNA Repair; D004267:DNA Viruses / Q000528:radiation effects; D004269:DNA, Bacterial / Q000528:radiation effects*; D004926:Escherichia coli / Q000187:drug effects / Q000528:radiation effects*; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D011743:Pyrimidines / Q000378:metabolism; D011831:Radiation Genetics; D013696:Temperature; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial; D011743:Pyrimidines; D009268:Nalidixic Acid; D002701:Chloramphenicol