Ribosomal RNA fingerprints reveal 3 domains of Life.

X-ray film 'fingerprint' rRNA. COURTESY OF NORMAN R. PACE, JAN SAPP, AND NIGEL GOLDENFELD. PNAS, 109:1011–18, 2012.

In 1969, Carl Woese, a microbiologist at the University of Illinois, wanted to use “the cell’s internal fossil record”- specifically, the ribosomal RNA of the cell’s translation machinery—“to extend our knowledge of evolution backward in time by a billion years or so.” Woese’s team had RNA sequencing up and running in the lab. Their protocol consisted of digestion and two-dimensional electrophoresis of radioactive small-subunit (16S or 18S) ribosomal RNA. When exposed to X-ray film, the separated fragments generated a unique fingerprint, which Woese interpreted based on the position of the spots.      After digestion of the spots, Woese determined the sequences of the oligonucleotide fragments - each about 6 to 14 - nucleotides long and recorded them on 80-column IBM punch cards. The team then compared the catalog of sequences from each organism using a computer program.      Woese's team sequenced ribosomal RNA from readily available lab strains of bacteria, and Woese grew to expect the same spots that appeared over and over again on the film. Their analysis of methanogens led to a eureka moment. Things they expected to find weren’t there... methanogen species were missing two distinct spots and also lacked fragments universal to previously examined bacteria. It became clear these organisms belonged to a distinct group.      In 1977, Woese's lab published a landmark paper proposing 3 distinct groups, which they described as “eukingdoms”: eubacteria, archaebacteria, and eukaryotes. Eventually it became widely accepted as the 3 Domains of Life.      Carl R. Woese and George E. Fox. Phylogenetic structure of the prokaryotic domain:    The primary kingdoms. PNAS 1977 74 (11) 5088-5090; doi:10.1073/pnas.74.11.5088 back  from Discovering Archaea by A.Olena 3/1/14 Scientist Mag.