title: Repair of single-strand deoxyribonucleic acid breaks in ultraviolet light-irradiated Haemophilus influenzae.
abstract: The wild-type strain and mutants of Haemophilus influenzae, sensitive or resistant to ultraviolet light (UV) as defined by colony-forming ability, were examined for their ability to perform the incision and rejoining steps of the deoxyribonucleic acid (DNA) dark repair process. Although UV-induced pyrimidine dimers are excised by the wild-type Rd and a resistant mutant BC200, the expected single-strand DNA breaks could not be detected on alkaline sucrose gradients. Repair of the gap resulting from excision must be rapid when experimental conditions described by us are employed. Single-strand DNA breaks were not detected in a UV-irradiated sensitive mutant (BC100) incapable of excising pyrimidine dimers, indicating that this mutant may be defective in a dimer-recognizing endonuclease. No single-strand DNA breaks were detected in a lysogen BC100(HP1c1) irradiated with a UV dose large enough to induce phage development in 80% of the cells.
mesh_terms: D001435:Bacteriophages; D002247:Carbon Isotopes; D002499:Centrifugation, Density Gradient; D004260:DNA Repair; D004267:DNA Viruses; D004269:DNA, Bacterial / Q000032:analysis / Q000096:biosynthesis* / Q000528:radiation effects; D004277:DNA, Single-Stranded / Q000032:analysis / Q000096:biosynthesis / Q000528:radiation effects; D006193:Haemophilus influenzae / Q000032:analysis / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D008242:Lysogeny; D009154:Mutation; D011830:Radiation Effects; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D002247:Carbon Isotopes; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D014316:Tritium; D013936:Thymidine