In vitro reassembly of active large ribosomal subunits of the halophilic archaebacterium Haloferax mediterranei.

The large ribosomal subunits of the halophilic archaebacterium Haloferax mediterranei have been reconstituted in vitro from the dissociated RNA and protein components. Efficient reassembly of particles fully active in poly(U)-directed polyphenylalanine synthesis requires a 2-h incubation at 42 degrees C in the presence of no less than 2.5 M concentrations of monovalent cations and of 60 mM magnesium. K+ and NH4+ ions are equally effective in promoting subunit reconstitution; however, maximal efficiency is attained when they are combined in a 1:2 molar ratio. The reassembly process requires no heat activation step, as under the appropriate ionic conditions it takes place spontaneously within the temperature range optimal for growth of H. mediterranei cells (40-45 degrees C).