Insensitivity of archaebacterial ribosomes to protein synthesis inhibitors. Evolutionary implications.

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 implications of these findings are discussed.