The effect on Sulfolobus solfataricus (an extremely thermoacidophilic archaebacterium) of selected inhibitors affecting reactions of the polypeptide elongation cycle has been tested by using poly(U) and poly(UG) directed cell-free systems. The results reveal a unique pattern of antibiotic sensitivity of Sulfolobus ribosomes with an inhibitory effect observed for only three of 60 compounds tested. Through comparison with suitable eubacterial and eukaryotic cell-free systems the insensitivity of Sulfolobus ribosomes to most inhibitors of protein synthesis appears to reflect a phylogenetic distinction of ribosome structure, rather than the high temperature conditions of the Sulfolobus assay system. In this respect ribosomes of thermoacidophilic archaebacteria differ not only from their eubacterial and eukaryotic counterparts, but also from ribosomes of archaebacteria belonging to the methanogenic-halophilic branch of the 'third' kingdom. The evolutionary imnplications of these findings are discussed.

A spermine‐dependent, polyphenylalanine‐synthesizing cell‐free system having an optimum activity at 75–85°C, has been developed from the extremely thermoacidophilic archaebacterium Caldariella acidophila. The C. acidophila system is totally insensitive to the EF‐Tu targeted antibiotics pulvomycin (at 40°C) and kirromycin (at 47–72°C) contrary to control systems derived from both mesophilic (Escherichia coli) and thermoacidophilic (Bacillus acidocaldarius) eubacteria. The archaebacterial EF‐Tu‐equivalent factor is also immunologically unrelated to eubacterial EF‐Tu and does not cross react with antibodies against Escherichia coli EF‐Tu. The pulvomycin and kirromycin reactions thus provide new phyletic markers for archaebacterial ancestry.

1. The ribosomal subunits of one thermoacidophilic archaebacterium (Caldariella acidophila) and of two reference eubacterial species (Bacillus acidocaldarius, Escherichia coli) were compared with respect to ribosome mass and protein composition by (i) equilibrium-density sedimentation of the particles in CsCl and (ii) gel-electrophoretic estimations of the molecular weights of the protein and the rRNA. 2. By either procedure, it is estimated that synthetically active archaebacterial 30S subunits (52% protein by wt.) are appreciably richer in protein than the corresponding eubacterial particles (31% protein by wt.) 3. The greater protein content of the archaebacterial 30S subunits is accounted for by both a larger number and a greater average molecular weight of the subunit proteins; specifically, C. acidophila 30S subunits yield 28 proteins whose combined mass is 0.6 X 10(6) Da, compared with 20 proteins totalling 0.35 X 10(6) Da mass for eubacterial 30S subunits. 4. No differences in protein number are detected among the large subunits, but C. acidophila 50S subunits exhibit a greater number-average molecular weight of their protein components than do eubacterial 50S particles. 5. Particle weights estimated by either buoyant-density data, or molecular weights of rRNA plus protein, agree to within less than 2%. By either procedure C. acidophila 30S subunits 1.15 X 10(6) Da mass) are estimated to be about 300 000 Da heavier than their eubacterial counterparts (0.87 X 10(6) Da mass); a smaller difference. 0.15 X 10(6) Da, exists between the archaebacterial and the eubacterial 50S subunits (respectively 1.8 X 10(6) and 1.65 X 10(6) Da). It is concluded that the heavier-than-eubacterial mass of the C. acidophila ribosomes resides principally in their smaller subunits.

No abstract

No abstract