Taken without permission from Biological Abstracts
on CD-ROM, for "fair use" only:
TI: Molecular classification of living organisms.
AU: Saccone-C; Gissi-C; Lanave-C; Pesole-G
CS: Dip. Biochim. Biol. Mol., Univ. di Bari, via Orabona,
4, 70126 Bari, Italy
SO: Journal of Molecular evolution 40(3): 273-279
PY: 1995
IS: 0022-2844
LA: English
AB: Recent studies in molecular evolution have
generated strong conflicts in opinion as to how world
living organisms should be classifed. The traditional
classification of life into five kingdoms has been
challenged by the molecular analysis carried out mostly
on rRNA sequences, which supported the division of the
extant living organisms into three major groups:
Archaebacteria, Eubacteria, and Eukaryota. As to the
problem of placing the root of the tree of life, the analysis
carried out on a few genes has provided discrepant
results. In order to measure the genetic distance between
species, we have carried out an evolutionary analysis of
the glutamine synthetase genes, which previously have
been revealed to be good molecular clocks, and of the
small and large rRNA genes. All the data demonstrate
that archaebacteria are more closely related to
eubacteria than to eukaryota, thus supporting tha
classical division of living organisms into two main
superkingdoms, Prokaryota and Eukaryota.
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JA: Biological Abstracts vol. 99 Iss. 11, ref. 155946
UD: 9502
TI: Root of the universal tree of life based on ancient
aminoacyl-tRNA synthetase gene duplications.
AU: Brown-J-R; Doolittle-W-F
CS: Canadian Inst. Advanced Res., Dep. Biochem.,
Dalhousie Univ., Sir Charles Tupper Build., Halifax, NS
B3H 4H7, Canada
SO: Procedings of the National Academy of Sciences of
the United States of America 92(7): 2441-2445
PY: 1995
IS: 0027-8424
LA: English
AB: Universal trees based on sequences of single gene
homologs cannot be rooted. Iwabe et al. (Iwabe, N.,
Kuma, K.-I., Hasegawa. M., Osawa, S. & Miyata, T.
(1989) Proc. Natl. Acad. Sci. USA 86, 9355-9359)
circumvented this problem by using ancient gene
duplications that predated the last common ancestor of
all living things. Their seperate, reciprocally rooted trees
for elongation factors and ATPase subunits subunits
showed Bacteria (eubacteria) as branching first from the
universal tree with Archaea (archaebacteria) and
Eukarya (eukaryotes) as sister groups. Given its topical
importance to evolutionary biology and concerns about
the appropriatness of the ATPase data set, an evaluation
of the universal tree using other ancient gene
duplications is essential. In this study, we derive a
rooting for the universal tree using aminoacyl-tRNA
synthetase genes, an extensive multigene family whose
divergence likely preceded that of prokaryotes and
eukaryotes. An approximatly 1600-bp conserved region
was sequenced from the isoleucyl-tRNA synthetases of
several species representing deep evolutionary branches
of eukaryotes (Nosema lucustae), Bacteria (Aquifex
pyrophilus and Thermotonga maritima) and Archae
(Pyrococcus furiosus and Sulfolobus acidocaldarius). In
addition, a new valyl-tRNA synthetase was characterized
from the protist Trichomonas vaginalis. Different
phylogenetic methods were used to generate trees of
isoleucyl-tRNA synthetase rooted valyl- and leucyl-tRNA
synthetases. All isoleucyl-tRNA synthetase trees show
Archaea and Eucarya as sister groups, providing strong
confirmation for the universal rooting reported by Iwabe
et al. As well, there was strong support for synthetase
gene from Tr. vaginalis clustered with other eukaryotic
ValRS genes, which may have been transferred from the
mitochondrial genome to the nuclear genome,
suggesting that this amitochondrial trichomonad once
harbored an endosymbiotic bacterium.
- - -
JA: Biological Abstracts vol. 99, Iss. 11, Ref. 151624
UD: 9502
I couldn't resist posting this. Sorry.
L.
