arlin at ac.dal.ca wrote:
: I'm puzzled as to why every month there appear research articles in
: which the most recent common ancestor of the known groups of cellular
: life is referred to as a "progenote" or "the progenote". For those
: who aren't familiar with this term, a "progenote" is a hypothetical
: type of organism (envisioned by Carl Woese), in which the
: genotype/phenotype relation is inexact-- modern cellular organisms are
: all "genotes". Progenotic replication, transcription, and translation
: are rudimentary and error-prone, which necessitates small genes and
: small segmented genomes, according to Woese (e.g., see "Bacterial
: Evolution", Microbiol. Rev. 51: 221-271.). Woese argued that
: progenotes must have been a necessary stage in the evolution of modern
: cellular life, and hypothesized that the ancestor of eubacteria,
: eukaryotes and archaebacteria was in fact such a progenote, even that
: this organism might have had an RNA genome.
: Hasn't sufficient evidence accumulated to formally reject this
: hypothesis? Forterre and colleagues [Biosystems (Netherlands) 28(1-3)
: p15-3] have argued persuasively that the existence of homologous
: DNA-polymerase genes with proofreading functions in all groups of
: cellular organisms rules out the possibility that the ancestor had an
: RNA genome or rudimentary error-prone replication. Archaebacteria and
: eubacteria (whose most recent common ancestor would be a common
: ancestor of all known cellular life according to various likely
: phylogenies) share conserved operon structures for RNA Polymerase
: subunit genes, as well as some genes for ribosomal proteins. This
: indicates that their most recent common ancestor must have had long
: DNA genes (i.e., not short gene-segments) arranged in operons (wow!).
: At least a dozen ribosomal proteins (as well as some translation
: factors) are shared by all cellular organisms [Wittmann-Liebold, et
: al., in _The Ribosome: Structure, Function and Evolution_, ed. W.
: Hill, et al. (American Society for Microbiology Press, Washington DC,
: 1990)], indicating that their most recent common ancestor must have
: had a rather complex polyfunctional (i.e., not 'rudimentary')
: ribosome. What gives?
One fact which I am not clear about since I haven't read the original
article. Did Woese imply that his progenote was the last common
ancestor of modern organisms? Many of the replies seem to be assuming
that he did. Yet the description seems to me to be compatible with it
being an early RNA form which then evolved into the last common
ancestor with its long DNA genes, highly evolved enzymes etc.
Can anyone help.
andrewh at uniwa.uwa.edu.au