title: Enzyme action at 3' termini of ionizing radiation-induced DNA strand breaks.
abstract: gamma-Irradiation of DNA in vitro produces two types of single strand breaks. Both types of strand breaks contain 5'-phosphate DNA termini. Some strand breaks contain 3'-phosphate termini, some contain 3'-phosphoglycolate termini (Henner, W.D., Rodriguez, L.O., Hecht, S. M., and Haseltine, W. A. (1983) J. Biol. Chem. 258, 711-713). We have studied the ability of prokaryotic enzymes of DNA metabolism to act at each of these types of gamma-ray-induced 3' termini in DNA. Neither strand breaks that terminate with 3'-phosphate nor 3'-phosphoglycolate are substrates for direct ligation by T4 DNA ligase. Neither type of gamma-ray-induced 3' terminus can be used as a primer for DNA synthesis by either Escherichia coli DNA polymerase or T4 DNA polymerase. The 3'-phosphatase activity of T4 polynucleotide kinase can convert gamma-ray-induced 3'-phosphate but not 3'-phosphoglycolate termini to 3'-hydroxyl termini that can then serve as primers for DNA polymerase. E. coli alkaline phosphatase is also unable to hydrolyze 3'-phosphoglycolate groups. The 3'-5' exonuclease actions of E. coli DNA polymerase I and T4 DNA polymerase do not degrade DNA strands that have either type of gamma-ray-induced 3' terminus. E. coli exonuclease III can hydrolyze DNA with gamma-ray-induced 3'-phosphate or 3'-phosphoglycolate termini or with DNase I-induced 3'-hydroxyl termini. The initial action of exonuclease III at 3' termini of ionizing radiation-induced DNA fragments is to remove the 3' terminal phosphate or phosphoglycolate to yield a fragment of the same nucleotide length that has a 3'-hydroxyl terminus. These results suggest that repair of ionizing radiation-induced strand breaks may proceed via the sequential action of exonuclease, DNA polymerase, and DNA ligase. The possible role of exonuclease III in repair of gamma-radiation-induced strand breaks is discussed.
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D001483:Base Sequence; D011088:DNA Ligases / Q000378:metabolism*; D004253:DNA Nucleotidylexotransferase / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D005090:Exodeoxyribonucleases / Q000378:metabolism; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D011116:Polynucleotide 5'-Hydroxyl-Kinase / Q000378:metabolism; D011118:Polynucleotide Ligases / Q000378:metabolism*; D013604:T-Phages / Q000201:enzymology
chemical_list: D009838:Oligodeoxyribonucleotides; C030570:oligodeoxyadenylic acid; D011116:Polynucleotide 5'-Hydroxyl-Kinase; D004253:DNA Nucleotidylexotransferase; D004259:DNA-Directed DNA Polymerase; D005090:Exodeoxyribonucleases; C020133:exodeoxyribonuclease III; D000469:Alkaline Phosphatase; D011088:DNA Ligases; D011118:Polynucleotide Ligases