title: Photoreactivatiion, excision, and strand-rejoining repair in R factor-containing minicells of Escherichia coli K-12.
abstract: Chromosomeless "minicells" are formed by misplaced cell fissions near the polar extremities of an Escherichia coli K-12 mutant strain. Resistance (R)-factor deoxyribonucleic acid (DNA) can be introduced into minicells by segregation from an R(+) (R64-11) derivative of the original mutant. We have assessed the ability of R(+) minicells to correct defects produced in their plasmid DNA by ultraviolet (UV) and gamma radiations. Minicells harboring plasmid DNA, in comparison with their repair-proficient minicell-producing parents, possess (i) an equal competence to rejoin single-strand breaks induced in DNA by gamma rays, (ii) a reduced capacity for the photoenzymatic repair of UV-induced pyrimidine dimers, and (iii) a total inability to excise dimers, apparently owing to a deficiency in UV-specific endonuclease activity responsible for mediating the initial incision step in excision repair. Assuming that the DNA repair properties of R(+) minicells reflect the concentration of repair enzymes located in the plasmid-containing polar caps of entire cells, these findings suggest that: (i) the enzymes responsible for rejoining single-strand breaks are distributed throughout the cell; (ii) photoreactivating enzyme molecules tend to be concentrated near bacterial DNA and to a lesser extent near plasmid DNA; and (iii) UV-specific endonuclease molecules are primarily confined to the central region of the E. coli cell and, thus, seldom segregate with R-factor DNA into minicells.
mesh_terms: D002470:Cell Survival; D002499:Centrifugation, Density Gradient; D003036:Cobalt Isotopes; D004254:DNA Nucleotidyltransferases; D004260:DNA Repair; D004269:DNA, Bacterial / Q000096:biosynthesis*; D003851:Deoxyribonucleases; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000201:enzymology / Q000302:isolation & purification / Q000378:metabolism / Q000528:radiation effects*; D005827:Genetics, Microbial; D007553:Isotope Labeling; D007700:Kinetics; D008190:Lyases; D010777:Photochemistry; D011742:Pyrimidine Nucleotides; D011830:Radiation Effects; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D003036:Cobalt Isotopes; D004269:DNA, Bacterial; D011742:Pyrimidine Nucleotides; D014316:Tritium; D004254:DNA Nucleotidyltransferases; D003851:Deoxyribonucleases; D008190:Lyases; D013936:Thymidine