W Ford Doolittle

Date:
[1980]
Reference:
PP/CRI/H/6/13/5
Catalogue details

Licence: In copyright

Credit: W Ford Doolittle. Source: Wellcome Collection.

    5/23
    This idea, and the evidence supporting it, stems directly from the work of Woese, Fox and collaborators [3,8-11 ]on the sequences of 16S and 18S ri bosomal RNAs (rRNAs). Comparisons, by numerical taxonornic techniques, of the catalogs of sequences of oligonucleotides derived from these molecules by T1-ribonuclease digestion, allow their division into three distinct classes; archaebacterial 16S, eubacterial 16S and nuclear- cytoplasmic 18S. Although there are internal divisions reflecting phylo- genetic divergence within each class, the classes do not overlap, and each can be further defined by a distinct set of highly-conservative oligo nucleotides {frequently showing distinctive post-transcriptional modifica tions) which presumably occupy functionally constrained regions of the molecule. The simplest interpretation is that given above; archaebacterial, eubacterial and nucíear-cytopiasmic lineages diverged at a time when problems of efficiency, speed and accuracy of translation were incompletely solved, and each lineage has achieved its own independent final solution. We can assume this time to have been at least 3.0 billion, and probably more, years ago, because recognizable blue-green algal fossils first appear at about that time [4], and there is ample evidence from both RNA and protein sequence data that there are divergences within the eubacteria themselves which predate the appearance of the blue-green algae [3,12,13]. There are objections to the radical phylogenetic revision proposed by Woese and Fox [3]. They are in part semantic. Woese and Fox call the three lineages primary kingdoms, and suggestions for taxonornic revision at this level are never easily accepted. The term archaebacteria unfortunately suggests that the members of this group are living fossils; the term eubacteria has an earlier and more limited taxonornic meaning [2],
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