Mechanism of thermotolerance induction by split-dose hyperthermia in Deinococcus radiodurans DNA repair deficient mutants

We examined the phenomenon of thermotolerance induction in the radioresistant prokaryote, Deinococcus radiodurans, which was initially exposed to 30 min at 52°C followed by various intervals up to 6 h at 30°C in TGY medium and then re-exposed to 52°C for various periods, i.e., split-dose hyperthermia. This thermotolerance induction was analyzed in DNA repair deficient mutants (strain 302, 251, UVS25, rec30 and KH840) and the wild-type strain MR 1 . The strain UVS25 is a double mutant for the mtcA and uvsD genes, and strain rec30 is a mutant for the deinococcal recA gene. The induction was suppressed to 1/10 and ½5 in strains UVS25 and rec30 respectively, as compared with the maximum level in the wild-type strain MR 1 . However, the induction in strain 302 (mutant for the uvrA gene) was not suppressed. Therefore, we conclude that proteins synthesized during the interexposure interval, i.e., the products of the uvsD (UV endonuclease β) and recA (RecA protein) genes contribute to the induction of thermotolerance in D. radiodurans.