Archaebacterial 5 S Ribosomal RNA

Abstract

The available information on primary and secondary structure of archaebacterial 5S rRNA is reviewed. The extent of primary sequence diversity is comparable to that seen among eubacterial genera. This is consistent with the view that the archaebacteria represent a taxon of the highest order among entities with procaryotic organization. The sequence information is also used to construct a phylogenetic tree which within the limitations of the data is in reasonable agreement with earlier results. In terms of secondary structure the archaebacterial 5 S rRNAs do not conform to the generally accepted models for either eubacterial or eucaryotic cytoplasmic 5S rRNAs. Instead there may be several classes of structures represented. Each of these would include a mixture of eubacterial features, eucaryotic features and unique features.

These findings are discussed as they relate to the evolutionary position of the archaebacteria. It is pointed out that lateral gene transfer may have been far more frequent in the earliest stages of evolution and it is argued that this could profoundly effect the way one interprets data pertaining to the phylogenetic position of the archaebacteria. It is also observed that future studies would benefit greatly by inclusion of a phylogenetically diverse selection of archaebacteria.