Radiation response in D einococcus deserti : IrrE is a metalloprotease that cleaves repressor protein DdrO

Summary D einococcus bacteria are famous for their extreme radiation tolerance. The IrrE protein was shown to be essential for radiation tolerance and, in an unelucidated manner, for induction of a number of genes in response to radiation, including recA and other DNA repair genes. Earlier studies indicated that IrrE could be a zinc peptidase, but proteolytic activity was not demonstrated. Here, using several in vivo and in vitro experiments, IrrE from D einococcus deserti was found to interact with DdrO , a predicted regulator encoded by a radiation‐induced gene that is, like irrE , highly conserved in D einococcus . Moreover, IrrE was found to cleave DdrO   in vitro and when the proteins were coexpressed in E scherichia coli . This cleavage was not observed in the presence of metal chelator EDTA or when IrrE contains a mutation in the conserved active‐site motif of metallopeptidases. In D . deserti , IrrE ‐dependent cleavage of DdrO was observed after exposure to radiation. Furthermore, DdrO ‐dependent repression of the promoter of a radiation‐induced gene was shown. These results demonstrate that IrrE is a metalloprotease and we propose that IrrE ‐mediated cleavage inactivates repressor protein DdrO , leading to transcriptional induction of various genes required for repair and survival after exposure of D einococcus to radiation.