title: The effects of microgravity on ligase activity in the repair of DNA double-strand breaks.
abstract: OBJECTIVE
  In recent years, contradictory data have been reported about the effects of microgravity on radiation-induced biological responses in space experiments. The aim of the present study was to clarify whether enzymatic repair of DNA double-strand breaks is affected by microgravity using an in vitro enzymatic reaction system.
  
  
  METHODS
  The DNA repair activity of T4 DNA ligase (EC 6.5.1.1) was measured in vitro for a DNA substrate damaged by restriction enzyme digestion during a US Space Shuttle mission (Discovery; STS-91). After the flight, the amount of ligated DNA molecules was measured using an electrophoresis method.
  
  
  RESULTS
  Ligated products (closed circular DNA, open circular DNA and multimeric ligated products) were produced by T4 DNA ligase treatment of linear DNA containing double-strand breaks, and they increased with increasing T4 DNA ligase concentration (0-3 units per microg of plasmid DNA). Almost no difference in T4 DNA ligase activity was detected between the space experiments and the control ground experiments.
  
  
  CONCLUSIONS
  No significant effect of microgravity on ligation of damaged DNA was found during space flight. Therefore, other mechanisms must account for the synergism between radiation and microgravity, if it exists.
authors.affiliation: Department of Biology, Nara Medical University, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Takahashi
authors.forename: K
authors.initials: K
authors.lastname: Ohnishi
authors.forename: S
authors.initials: S
authors.lastname: Takahashi
authors.forename: M
authors.initials: M
authors.lastname: Masukawa
authors.forename: K
authors.initials: K
authors.lastname: Sekikawa
authors.forename: T
authors.initials: T
authors.lastname: Amano
authors.forename: T
authors.initials: T
authors.lastname: Nakano
authors.forename: S
authors.initials: S
authors.lastname: Nagaoka
authors.forename: T
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D004249:DNA Damage; D011088:DNA Ligases / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D010957:Plasmids / Q000378:metabolism / Q000528:radiation effects; D013026:Space Flight; D014893:Weightlessness
chemical_list: D011088:DNA Ligases