MOLECULAR CLASSIFICATION OF LIVING ORGANISMS

Recent studies in molecular evolution have generated strong conflicts in opinion as to how world living organisms should be classified. The traditional classification of life into five kingdoms has been challen ged by the molecular analysis carried out mostly on rRNA sequences, wh ich supported the division of the extant living organisms into three m ajor groups: Archaebacteria, Eubacteria, and Eukaryota. As to the prob lem of placing the root of the tree of life, the analysis carried out on a few genes has provided discrepant results. In order to measure th e genetic distances between species, we have carried out an evolutiona ry analysis of the glutamine synthetase genes, which previously have b een revealed to be good molecular clocks, and of the small and large r RNA genes. All data demonstrate that archaebacteria are more closely r elated to eubacteria than to eukaryota, thus supporting the classical division of living organisms into two main superkingdoms, Prokaryota a nd Eukaryota.