CONSTRUCTION AND ANALYSIS OF A RECOMBINATION-DEFICIENT (RADA) MUTANT OF HALOFERAX-VOLCANII

By deleting the radA open reading frame of an extreme halophile, Halof erax volcanii, we created and characterized a recombination-deficient archaeon. This strain, Hf. volcanii DS52, has no detectable DNA recomb ination, is more sensitive to DNA damage by UV light and ethylmethane sulfonate, and has a slower growth rate than the wild type. These char acteristics are similar to those observed in recombination mutants of Eukarya and Bacteria, and show that the radA gene belongs in the recA/ RAD51 family by function as well as sequence homology. In addition, st rain DS52 was not transformable by plasmids pWL102 or pUBP2 (which con tain pHV2 and pHH1 replicons, respectively), although it was readily t ransformed by plasmids containing a pHK2 replicon, indicating a role f or radA in the maintenance or replication of some halobacterial plasmi ds. Despite its slower growth rate, Hf. volcanii DS52 was still easy t o culture and transform, and should be suitable for use in studies whe re a recombination-deficient background is desired.