Otsuka J.; Miyazaki K.; Horimoto K.
Department of Applied Biological Science, Faculty of Science
and Technology, Science University of Tokyo, Noda, Japan.
Divergence pattern and selective mode in protein evolution:
the example of vertebrate myoglobins and hemoglobin chains.
J Mol Evol. 1993 Feb; 36(2): 153-81.
The evolutionary relation of vertebrate myoglobin and the
hemoglobin chains including the agnathan hemoglobin chain is
investigated on the basis of a new view of amino acid
changes that is developed by canonical discriminant analysis
of amino acid residues at individual sites. In contrast to
the clear discrimination of amino acid residues between
myoglobin, hemoglobin alpha chain, and hemoglobin beta chain
in warm-blood vertebrates, the three types of globins in the
lower class of vertebrates show so much variation that they
are not well discriminated. This is seen particularly at the
sites that are ascertained in mammals to carry the amino
acid residues participating in stabilizing the monomeric
structure in myoglobin and the residues forming the subunit
contacts in hemoglobin. At these sites, agnathan hemoglobin
chains are evaluated to be intermediate between the
myoglobin and hemoglobin chains of gnathostomes. The
variation in the phylogenetically lower class of globins is
also seen in the internal region; there the amino acid
residues of myoglobin and hemoglobin chains in the
phylogenetically higher class exhibit an example of parallel
evolution at the molecular level. New quantities, the
distance of sequence property between discriminated groups
and the variation within each group, are derived from the
values of discriminant functions along the peptide chain,
and this set of quantities simply describes an overall
feature of globins such that the distinction between the
three types of globins has been clearer as the vertebrates
have evolved to become jawed, landed, and warm-blooded. This
result strongly suggests that the functional constraint on
the amino acid sequence of a protein is changed by living
conditions and that severe conditions constitute a driving
force that creates a distinctive protein from a less-
Stock D W.; Whitt G S.
Department of Ecology, Ethology, and Evolution, University of
Illinois, Urbana 61801.
Evidence from 18S ribosomal RNA sequences that lampreys and
hagfishes form a natural group.
Science. 1992 Aug 7; 257(5071): 787-9.
Lampreys and hagfishes (cyclostomes) traditionally were
considered to be a natural (monophyletic) group. Recently,
the consensus of opinion, based largely on morphological
analyses, has shifted to a view that lampreys are more
closely related to jawed vertebrates (gnathostomes) than to
hagfishes. Phylogenetic comparisons of 18S ribosomal RNA
sequences from two hagfishes, two lampreys, a tunicate, a
lancelet, and a number of gnathostomes support the monophyly
of the cyclostomes. These data force a reassessment of
several features of early vertebrate evolution.