The effects of microgravity on ligase activity in the repair of DNA double-strand breaks

Purpose: In recent years, contradictory data have been reported about the e ffects of microgravity on radiation-induced biological responses in space e xperiments. The aim of the present study was to clarify whether enzymatic r epair of DNA double-strand breaks is affected by microgravity using an in v itro enzymatic reaction system. Materials and 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 d igestion during a US Space Shuttle mission (Discovery; STS-91). After the f light, the amount of ligated DNA molecules was measured using an electropho resis method. Results: Ligated products (closed circular DNA, open circular DNA and multi meric 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 mu g of plasmid DNA). Almost no dif ference in T4 DNA ligase activity was detected between the space experiment s and the control ground experiments. Conclusions: No significant effect of microgravity on ligation of damaged D NA was found during space flight. Therefore, other mechanisms must account for the synergism between radiation and microgravity, if it exists.