Phylogenetic structure of the prokaryotic domain: The primary kingdoms

A phylogenetic analysis based upon ribosomal RNA sequence characterization reveals that living systems represent one of three aboriginal lines of descent: ( i ) the eubacteria, comprising all typical bacteria; ( ii ) the archaebacteria, containing methanogenic bacteria; and ( iii ) the urkaryotes, now represented in the cytoplasmic component of eukaryotic cells.