Here are my 5 cents worth of opinion concerning the Postinggs from L.A. Maron <CnsIqJ.MDz at gpu.utcc.utoronto.ca> lamoran at gpu.utcc.utoronto.ca (L.A. Moran):
There are many characters (not only 16S rRNAs) which separate Archae- and
Eubacteria (see Zillig et al., 1992, for a listing). With many molecular markers the
Archaebacteria appear closer to the Eukaryotes (e.g.: ATPases, elongation factors,
RNA polymerases). Not all of these molecular markers show the Archaebacteria as a
monophyletic group, in some analyses they appear paraphyletic; however, the branch
that separates the two archaebacterial groups is very short (as is the branch that
connects the 16S rRNA of the Archaebacteria to the other 16SrRNAs). Based only on
nucleotide data it will be difficult to discriminate between the para and monophyletic
origin of the archaebacteria. Rivera and Lake report a higher order character (a
deletion/insertion) that unites only some of the archaebacteria with the eukaryotes.
I think that one of the main problems in understanding the early evolution is the paradigm
of a tree (Hilario and Gogarten, 1993). The data reported by Zillig et al. (1992) and
Gupta and Golding (1993) suggest that not only the archaebacteria but also the
eubacteria made an early (i.e. before the mitochondria) and significant contribution to
the eukaryotic cell. There are many potential cases for horizontal gene transfer
(reviewed by Smith and Doolittle, 1993); however, not only single genes and operons
were transferred between species, it is likely that the merger of formerly independent
lineages to form a new species is not restricted to higher plants and the known cases of
endosymbiosis, but the merger of independent lineages occurred (and occurs)
throughout the evolution.
The eukaryotes almost certainly received major contributions from Archae- (Gogarten
et al. 1989, Iwabe et al. 1989) and Eubacteria (Zillig et al. 1992, Gupta et al.1993) In
addition, the glutamine synthetase (Kumada et al. 1993, Tiboni et al. 1993) and the
"HSP70" data suggest that also the Archaebacteria (or at least the mesophilic
Archaebacteria) received genes from gram positive eubacteria). In order to confirm
that these horizontal transfers do not represent separate events of horizontal gene
transfer but the merger of independent lineages more sufficiently resolved molecular
phylogenies would be needed.
J.Peter Gogarten
Gogarten at uconnvm.uconn.edu
Gogarten JP, Kibak H, Dittrich P, Taiz L, Bowman EJ, Bowman BJ, Manolson MF,
Poole RJ, Date T, Oshima T, Konishi J, Denda K, Yoshida M (1989) Evolution of the
vacuolar H+ - ATPase: Implications for the origin of eukaryotes. Proc Natl Acad Sci
USA 86: 6661 - 6665
Gupta RH, Golding GB (1993) Evolution of HSP70 gene and its implications
regarding relationships between archaebacteria, eubacteria and eukaryotes. J Mol Evol
37:573-582
Hilario E, Gogarten JP (1993) Horizontal Transfer of ATPase Genes -The Tree of
Life becomes a Net of Life. BioSystems 31, 111-119
Iwabe N, Kuma K-I, Hasegawa M, Osawa S, Miyata T (1989) Evolutionary
relationships of archaebacteria, eubacteria and eukaryotes inferred from phylogenetic
trees of duplicated genes. Proc Natl Acad Sci USA 86, 93559359
Kumada Y, Benson DR, Hillemann D, Hosted TJ, Rochford DA, Thompson CJ,
Wohlleben W, Tateno Y (1993) Evolution of the glutamine synthase gene, one of
the oldest existing and functioning genes. Proc Natl Acad Sci USA 90: 3009-3013
Rivera-MC Lake-JA (1992) Evidence that Eukaryotes and Eocyte Prokaryotes are immediate relatives.
Science 257, 74-76
Smith MW, Feng, D.F., Doolittle, R.F. (1992) Evolution by acquisition: the case for
horizontal gene transfer. Trends Biochem. Sci. 17, 489-493
Tiboni O, Cammarano P, Sanangelantoni AM (1993) Cloning and sequencing of the
gene encoding glutamine synthase I from the archaeum Pyrococcus woesei:
Anomalous phylogenies inferred from analysis of archaeal and bacterial glutamine
synthase I sequences. J Bacteriol 175: 2961-2969
Zillig W, Palm P, Klenk H-P (1992) A model of the early evolution of organisms:
The arisal of the three domains of life from the common ancestor. In: H Hartman,
K Matsuno (eds) The origin and evolution of the cell (World Scientific, Singapore,
New Jersey, London, Hong Kong) pp. 163182.
