Modification of survival after ultraviolet light exposure in a wild-type and a polA strain of Escherichia coli B/r by preirradiation treatment with chloramphenicol or rifampin.
The shoulder of the UV fluence-survival curve of exponentially growing Escherichia coli B/r WP2 trpE65 was expanded by chloramphenicol pretreatment and an exponential segment with intermediate slope appeared between the shoulder and the final exponential segment. These changes were dependent on DNA replication. The transitions with UV exposure to increased slopes were ascribed to UV inactivation of qualitatively different repair systems, each dependent upon the accumulation in each bacterium of multiple DNA-containing redundant repair components, which must be inactivated before the respective transitions to decreased resistance occur. Rifampin, which blocks DNA-dependent RNA polymerase function, limited drastically expansion of the shoulder and development of the intermediate exponential slope. Bacteria defective in DNA polymerase I (polA) showed only a slight expansion of the shoulder with pretreatment with chloramphenicol. Since certain bacterial plasmids require RNA primer formation for initiation of replication and are not maintained in a polA strain, it is proposed that the chloramphenicol-promoted increase in resistance depends on the formation of multiple numbers of specific resistance episomes (called repairons in view of their role in DNA repair).
D002701:Chloramphenicol / Q000494:pharmacology; D004256:DNA Polymerase I / Q000235:genetics; D004260:DNA Repair / Q000187:drug effects* / Q000528:radiation effects; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D012293:Rifampin / Q000494:pharmacology; D014466:Ultraviolet Rays
D004269:DNA, Bacterial; D002701:Chloramphenicol; D004256:DNA Polymerase I; D012293:Rifampin