title: Enzymic mechanism of excision-repair in T4-infected cells.
abstract: Excision of pyrimidine dimers from ultraviolet-irradiated DNA in a cell-free system of Escherichia coli infected with bacteriophage T4 consists of two different steps, one to induce a single-strand break at a point close to a pyrimidine dimer and the other to release dimer-containing nucleotide from the DNA. The enzymes responsible for these steps were isolated and the reactions were characterized; T4 endonuclease V introduces a break at the 5' side of a dimer and 5' in equilibrium 3' exonucleases, which are also induced by T4, act at the break to excise dimer-containing nucleotides. We isolated temperature-dependent v mutants, which exhibit increased sensitivity to UV at 42 degrees C but not at 30 degrees C, and found that the mutants induce temperature-sensitive T4 endonuclease V, indicating that the v gene of T4 is indeed the structural gene for T4 endonuclease V and that the enzyme is responsible for the first step of excision-repair. A possible mechanism of excision-repair in T4-infected cells is discussed.
mesh_terms: D003090:Coliphages / Q000378:metabolism*; D004260:DNA Repair; D004267:DNA Viruses / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism / Q000528:radiation effects*; D004270:DNA, Circular / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism / Q000528:radiation effects*; D003851:Deoxyribonucleases / Q000378:metabolism; D004720:Endonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D011742:Pyrimidine Nucleotides / Q000378:metabolism; D011830:Radiation Effects; D013941:Thymine / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial; D004270:DNA, Circular; D004279:DNA, Viral; D011742:Pyrimidine Nucleotides; D003851:Deoxyribonucleases; D004720:Endonucleases; D013941:Thymine