TOTAL RECONSTITUTION OF ACTIVE SMALL RIBOSOMAL-SUBUNITS OF THE EXTREME HALOPHILIC ARCHAEON HALOFERAX-MEDITERRANEI

The small ribosomal subunit of the halophilic archaeon Haloferax medit erranei has been reconstituted from its dissociated rRNA and protein c omponents. Efficient reconstitution of particles, fully active in poly (U)-dependent polyphenylalanine synthesis, occurs after 2 h of incubat ion at 36 degrees C in the presence of 1.5 M of (NH4)(2)SO4, 100 mM of MgAc2, 20 mM Tris-HCl (pH 8.2) and 6 mM 2-mercaptoethanol. Important differences in the optimal ionic conditions for the reconstitution of the 30S and the 50S ribosomal subunits from Haloferax mediterranei hav e been found. K+ and NH4+ ions have differing abilities to promote the reconstitution of the particles. The assembly of 30S ribosomal subuni ts of H. mediterranei has a higher tolerance to ionic strength than th e assembly of the 50S subunits and it is independent of the Mg2+ conce ntration present in the system.