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1.
Annexin homologues in the kingdoms of Planta and Protista were characterized by molecular sequence analysis to determine
their phylogenetic and structural relationship with annexins of Animalia. Sequence fragments from 19 plant annexins were identified
in sequence databases and composite sequences were also assembled from expressed sequence tags for Arabidopsis thaliana. Length differences in protein amino-termini and evidence for unique exon splice sites indicated that plant annexins were
distinct from those of animals. A third annexin gene of Giardia lamblia (Anx21-Gla) was identified as a distant relative to other protist annexins and to those of higher eukaryotes, thus providing a suitable
outgroup for evolutionary reconstruction of the family tree. Rooted evolutionary trees portrayed protist, plant, and Dictyostelium annexins as early, monophyletic ramifications prior to the appearance of closely related animal annexin XIII. Molecular phylogenetic
analyses of DNA and protein sequence alignments revealed at least seven separate plant subfamilies, represented by Anx18 (alfalfa, previously classified), Anx22 (thale cress), Anx23 (thale cress, cotton, rape and cabbage), Anx24 (bell pepper and tomato p34), Anx25 (strawberry, horseradish, pea, soybean, and castor bean), Anx26-Zma, and Anx27-Zma (maize). Other unique subfamilies may exist for rice, tomato p35, apple, and celery annexins. Consensus sequences compiled
for each eukaryotic kingdom showed some breakdown of the ``annexin-fold' motif in repeats 2 and 3 of protist and plant annexins
and a conserved codon deletion in repeat 3 of plants. The characterization of distinct annexin genes in plants and protists
reflects their comparable diversity among animal species and offers alternative models for the comparative study of structure–function
relationships within this important gene family.
Received: 30 May 1996 / Accepted: 20 August 1996 相似文献
2.
Plant genomes encode a variety of protein kinases, and while some are functional homologues of animal and fungal kinases,
others have a novel structure. This review focuses on three groups of unusual membrane-associated plant protein kinases: receptor-like
protein kinases (RLKs), calcium-dependent protein kinases (CDPKs), and histidine protein kinases.
Animal RLKs have a putative extracellular domain, a single transmembrane domain, and a protein kinase domain. In plants, all
of the RLKs identified thus far have serine/threonine signature sequences, rather than the tyrosine-specific signature sequences
common to animals. Recent genetic experiments reveal that some of these plant kinases function in development and pathogen
resistance.
The CDPKs of plants and protozoans are composed of a single polypeptide with a protein kinase domain fused to a C-terminal
calmodulin-like domain containing four calcium-binding EF hands. No functional plant homologues of protein kinase C or Ca2+/calmodulin-dependent protein kinase have been identified, and no animal or fungal CDPK homologues have been identified.
Recently, histidine kinases have been shown to participate in signaling pathways in plants and fungi. ETR1, an Arabidopsis histidine kinase homologue with three transmembrane domains, functions as a receptor for the plant hormone ethylene. G-protein-coupled
receptors, which often serve as hormone receptors in animal systems, have not yet been identified in plants.
Received: 18 August 1997/Revised: 23 December 1997 相似文献
3.
4.
Diversity, Distribution, and Ancient Taxonomic Relationships Within the TIR and Non-TIR NBS-LRR Resistance Gene Subfamilies 总被引:1,自引:0,他引:1
Cannon SB Zhu H Baumgarten AM Spangler R May G Cook DR Young ND 《Journal of molecular evolution》2002,54(4):548-562
Phylogenetic relationships among the NBS-LRR (nucleotide binding site–leucine-rich repeat) resistance gene homologues (RGHs)
from 30 genera and nine families were evaluated relative to phylogenies for these taxa. More than 800 NBS-LRR RGHs were analyzed,
primarily from Fabaceae, Brassicaceae, Poaceae, and Solanaceae species, but also from representatives of other angiosperm
and gymnosperm families. Parsimony, maximum likelihood, and distance methods were used to classify these RGHs relative to
previously observed gene subfamilies as well as within more closely related sequence clades. Grouping sequences using a distance
cutoff of 250 PAM units (point accepted mutations per 100 residues) identified at least five ancient sequence clades with
representatives from several plant families: the previously observed TIR gene subfamily and a minimum of four deep splits
within the non-TIR gene subfamily. The deep splits in the non-TIR subfamily are also reflected in comparisons of amino acid
substitution rates in various species and in ratios of nonsynonymous-to-synonymous nucleotide substitution rates (K
A/K
S values) in Arabidopsis thaliana. Lower K
A/K
S values in the TIR than the non-TIR sequences suggest greater functional constraints in the TIR subfamily. At least three
of the five identified ancient clades appear to predate the angiosperm–gymnosperm radiation. Monocot sequences are absent
from the TIR subfamily, as observed in previous studies. In both subfamilies, clades with sequences separated by approximately
150 PAM units are family but not genus specific, providing a rough measure of minimum dates for the first diversification
event within these clades. Within any one clade, particular taxa may be dramatically over- or underrepresented, suggesting
preferential expansions or losses of certain RGH types within particular taxa and suggesting that no one species will provide
models for all major sequence types in other taxa.
Received: 13 June 2001 / Accepted: 22 October 2001 相似文献
5.
Geneviàve Pont-Kingdon Norichika A. Okada Jane L. Macfarlane C. Timothy Beagley Cristi D. Watkins-Sims Thomas Cavalier-Smith G. Desmond Clark-Walker David R. Wolstenholme 《Journal of molecular evolution》1998,46(4):419-431
The nucleotide sequences of two segments of 6,737 ntp and 258 ntp of the 18.4-kb circular mitochondrial (mt) DNA molecule
of the soft coral Sarcophyton glaucum (phylum Cnidaria, class Anthozoa, subclass Octocorallia, order Alcyonacea) have been determined. The larger segment contains
the 3′ 191 ntp of the gene for subunit 1 of the respiratory chain NADH dehydrogenase (ND1), complete genes for cytochrome
b (Cyt b), ND6, ND3, ND4L, and a bacterial MutS homologue (MSH), and the 5′ terminal 1,124 ntp of the gene for the large subunit rRNA (l-rRNA). These genes are arranged in the order given
and all are transcribed from the same strand of the molecule. The smaller segment contains the 3′ terminal 134 ntp of the
ND4 gene and a complete tRNAf-Met gene, and these genes are transcribed in opposite directions. As in the hexacorallian anthozoan, Metridium senile, the mt-genetic code of S. glaucum is near standard: that is, in contrast to the situation in mt-genetic codes of other invertebrate phyla, AGA and AGG specify
arginine, and ATA specifies isoleucine. However, as appears to be universal for metazoan mt-genetic codes, TGA specifies tryptophan
rather than termination. Also, as in M. senile the mt-tRNAf-Met gene has primary and secondary structural features resembling those of Escherichia coli initiator tRNA, including standard dihydrouridine and TψC loop sequences, and a mismatched nucleotide pair at the top of
the amino-acyl stem. The presence of a mutS gene homologue, which has not been reported to occur in any other known mtDNA, suggests that there is mismatch repair activity
in S. glaucum mitochondria. In support of this, phylogenetic analysis of MutS family protein sequences indicates that the S. glaucum mtMSH protein is more closely related to the nuclear DNA-encoded mitochondrial mismatch repair protein (MSH1) of the yeast
Saccharomyces cerevisiae than to eukaryotic homologues involved in nuclear function, or to bacterial homologues. Regarding the possible origin of
the S. glaucum mtMSH gene, the phylogenetic analysis results, together with comparative base composition considerations, and the absence of an
MSH gene in any other known mtDNA best support the hypothesis that S. glaucum mtDNA acquired the mtMSH gene from nuclear DNA early in the evolution of octocorals. The presence of mismatch repair activity in S. glaucum mitochondria might be expected to influence the rate of evolution of this organism's mtDNA.
Received: 13 January 1997 / Accepted: 23 September 1997 相似文献
6.
Karen Miller Clare Lynch Joanne Martin Elisabeth Herniou Michael Tristem 《Journal of molecular evolution》1999,49(3):358-366
Gypsy LTR-retrotransposons have been identified in the genomes of many organisms, but only a small number of vertebrate examples
have been reported to date. Here we show that members of this family are likely to be widespread in many vertebrate classes
with the possible exceptions of mammals and birds. Phylogenetic analyses demonstrate that although there are several distinct
lineages of vertebrate gypsy LTR-retrotransposons, the majority clusters into one monophyletic clade. Groups of fungal, plant, and insect elements were
also observed, suggesting horizontal transfer between phyla may be infrequent. However, in contrast to this, there was little
evidence to support sister relationships between elements derived from vertebrate and insect hosts. In fact, the majority
of the vertebrate elements appeared to be most closely related to a group of gypsy LTR-retrotransposons present within fungi. This implies either that at least one horizontal transmission between these two
phyla has occurred previously or that a gypsy LTR-retrotransposon lineage has been lost from insect taxa.
Received: 22 December 1998 / Accepted: 6 April 1999 相似文献
7.
Hiroshi Suga Daisuke Hoshiyama Shigehiro Kuraku Kazutaka Katoh Kaoru Kubokawa Takashi Miyata 《Journal of molecular evolution》1999,49(5):601-608
Animals evolved a variety of gene families involved in cell–cell communication and developmental control by gene duplication
and domain shuffling. Each family is made up of several subtypes or subfamilies with distinct structures and functions, which
diverged by gene duplications and domain shufflings before the divergence of parazoans and eumetazoans. Since the separation
from protostomes, vertebrates expanded the multiplicity of members (isoforms) in the same subfamily by further gene duplications
in their early evolution before the fish–tetrapod split. To know the dates of isoform duplications more closely, we have conducted
isolation and sequencing cDNAs encoding the fibroblast growth factor receptor, Eph, src, and platelet-derived growth factor receptor subtypes belonging to the protein tyrosine kinase family from Branchiostoma belcheri, an amphioxus, Eptatretus burgeri, a hagfish, and Lampetra reissneri, a lamprey. From a phylogenetic tree of each subfamily inferred from a maximum likelihood (ML) method, together with a bootstrap
analysis based on the ML method, we have shown that the isoform duplications frequently occurred in the early evolution of
vertebrates around or just before the divergence of cyclostomes and gnathostomes by gene duplications and possibly chromosomal
duplications.
Received: 28 April 1998 / Accepted: 30 June 1999 相似文献
8.
Carolyn J. Lawrence Russell L. Malmberg Michael G. Muszynski R. Kelly Dawe 《Journal of molecular evolution》2002,54(1):42-53
We have reconstructed the evolution of the anciently derived kinesin superfamily using various alignment and tree-building
methods. In addition to classifying previously described kinesins from protists, fungi, and animals, we analyzed a variety
of kinesin sequences from the plant kingdom including 12 from Zea mays and 29 from Arabidopsis thaliana. Also included in our data set were four sequences from the anciently diverged amitochondriate protist Giardia lamblia. The overall topology of the best tree we found is more likely than previously reported topologies and allows us to make the
following new observations: (1) kinesins involved in chromosome movement including MCAK, chromokinesin, and CENP-E may be
descended from a single ancestor; (2) kinesins that form complex oligomers are limited to a monophyletic group of families;
(3) kinesins that crosslink antiparallel microtubules at the spindle midzone including BIMC, MKLP, and CENP-E are closely
related; (4) Drosophila NOD and human KID group with other characterized chromokinesins; and (5) Saccharomyces SMY1 groups with kinesin-I sequences, forming a family of kinesins capable of class V myosin interactions. In addition, we
found that one monophyletic clade composed exclusively of sequences with a C-terminal motor domain contains all known minus
end-directed kinesins.
Received: 20 February 2001 / Accepted: 5 June 2001 相似文献
9.
The single-copy actin gene of Giardia lamblia lacks introns; it has an average of 58% amino acid identity with the actin of other species; and 49 of its amino acids can be aligned with the amino acids of a consensus sequence of heat shock protein 70. Analysis of the potential RNA secondary structure in the transcribed region of the G. lamblia actin gene and of the single-copy actin gene of nine other species did not reveal any conserved structures. The G. lamblia actin sequence was used to root the phylogenetic trees based on 65 actin protein sequences from 43 species. This tree is congruent with small-subunit rRNA trees in that it shows that oomycetes are not related to higher fungi; that kinetoplatid protozoans, green plants, fungi and animals are monophyletic groups; and that the animal and fungal lineages share a more recent common ancestor than either does with the plant lineage. In contrast to smalls-ubunit rRNA trees, this tree shows that slime molds diverged after the plant lineage. The slower rate of evolution of actin genes of slime molds relative to those of plants, fungi, and animals species might be responsible for this incongruent branching.
Correspondence to: G. Drouin 相似文献
10.
Primary Structure and Phylogenetic Relationships of a Malate Dehydrogenase Gene from Giardia lamblia
The lactate and malate dehydrogenases comprise a complex protein superfamily with multiple enzyme homologues found in eubacteria,
archaebacteria, and eukaryotes. In this study we describe the sequence and phylogenetic relationships of a malate dehydrogenase
(MDH) gene from the amitochondriate diplomonad protist, Giardia lamblia. Parsimony, distance, and maximum-likelihood analyses of the MDH protein family solidly position G. lamblia MDH within a eukaryote cytosolic MDH clade, to the exclusion of chloroplast, mitochondrial, and peroxisomal homologues. Furthermore,
G. lamblia MDH is specifically related to a homologue from Trichomonas vaginalis. This MDH topology, together with published phylogenetic analyses of β-tubulin, chaperonin 60, valyl-tRNA synthetase, and
EF-1α, suggests a sister-group relationship between diplomonads and parabasalids. Since these amitochondriate lineages contain
genes encoding proteins which are characteristic of mitochondria and α-proteobacteria, their shared ancestry suggests that
mitochondrial properties were lost in the common ancestor of both groups.
Received: 14 September 1998 / Accepted: 29 December 1998 相似文献
11.
Among Bacteria the carA and carB genes encoding the small (CarA) and large (CarB) subunits of carbamoylphosphate synthase (CPS) have been lost in certain
symbionts (Haemophylus influenzae) and in most obligate intracellular parasites (Chlamydiae, Spirochaetes, Mycoplasmatales, Rickettsiae) having genome sizes in the 0.7- to 1.1-Mb range. Compared to Bacteria, Archaea exhibit a more varied pattern of CPS gene
losses and an unusual propensity to incorporate CPS genes derived from both Bacteria and other Archaea. Schematically they
fall into three groups. Group 1 taxa (the crenarchaeon Aeropyrum pernix and the euryarchaea Pyrococcus horikoshi and Pyrococcus abyssii) lack CPS genes altogether. Group 2 taxa (comprising Halobacteriales, Thermoplasmales, Methanococcales, Methanomicrobiales,
Archaeoglobales) harbor CPS genes whose encoded CarB and CarA subunit proteins are ostensibly bacterial in origin; that is,
they are intermixed with bacterial homologues on a phylogeny of concatenated CarA and CarB sequences and are not distinguishable
from bacterial sequences after searching for domain-specific amino acid residue positions. Group 3 taxa (the crenarchaea Pyrobaculum aerophilum, Sulfolobus solfataricus, and Sulfolobus tokodaii and the euryarchaeon Pyrococcus furiosus) harbor CPS genes whose encoded proteins appear to be archaeal: consistent with an archaeal origin, the CarA and CarB sequences
in this group possess both unique signatures and signatures affiliating them to Eukarya. Based on the topology of the clade
comprising the four Group 3 taxa, we argue that CPS genes of P. furiosus (a euryarchaeon) and those of the crenarchaea P. aerophilum, S. solfataricus, and S. tokodaii are of a single type, resulting from the two genes being laterally transferred from a crenarchaeon to P. furiosus. 相似文献
12.
Jürgen Wastl Martin Fraunholz Stefan Zauner Susan Douglas Uwe-G. Maier 《Journal of molecular evolution》1999,48(1):112-117
Cryptomonads, small biflagellate algae, contain four different genomes. In addition to the nucleus, mitochondrion, and chloroplast
is a fourth DNA-containing organelle the nucleomorph. Nucleomorphs result from the successive reduction of the nucleus of
an engulfed phototrophic eukaryotic endosymbiont by a secondary eukaryotic host cell. By sequencing the chloroplast genome
and the nucleomorph chromosomes, we identified a groEL homologue in the genome of the chloroplast and a related cpn60 in one of the nucleomorph chromosomes. The nucleomorph-encoded Cpn60 and the chloroplast-encoded GroEL correspond in each
case to one of the two divergent GroEL homologues in the cyanobacterium Synechocystis sp. PCC6803. The coexistence of divergent groEL/cpn60 genes in different genomes in one cell offers insights into gene transfer from evolving chloroplasts to cell nuclei and
convergent gene evolution in chlorophyll a/b versus chlorophyll a/c/phycobilin eukaryotic lineages.
Received: 24 April 1998 / Accepted: 12 June 1998 相似文献
13.
Heat Shock Protein 70 Family: Multiple Sequence Comparisons, Function, and Evolution 总被引:14,自引:0,他引:14
The heat shock protein 70 kDa sequences (HSP70) are of great importance as molecular chaperones in protein folding and transport.
They are abundant under conditions of cellular stress. They are highly conserved in all domains of life: Archaea, eubacteria,
eukaryotes, and organelles (mitochondria, chloroplasts). A multiple alignment of a large collection of these sequences was
obtained employing our symmetric-iterative ITERALIGN program (Brocchieri and Karlin 1998). Assessments of conservation are
interpreted in evolutionary terms and with respect to functional implications. Many archaeal sequences (methanogens and halophiles)
tend to align best with the Gram-positive sequences. These two groups also miss a signature segment [about 25 amino acids
(aa) long] present in all other HSP70 species (Gupta and Golding 1993). We observed a second signature sequence of about 4
aa absent from all eukaryotic homologues, significantly aligned in all prokaryotic sequences. Consensus sequences were developed
for eight groups [Archaea, Gram-positive, proteobacterial Gram-negative, singular bacteria, mitochondria, plastids, eukaryotic
endoplasmic reticulum (ER) isoforms, eukaryotic cytoplasmic isoforms]. All group consensus comparisons tend to summarize better
the alignments than do the individual sequence comparisons. The global individual consensus ``matches' 87% with the consensus
of consensuses sequence. A functional analysis of the global consensus identifies a (new) highly significant mixed charge
cluster proximal to the carboxyl terminus of the sequence highlighting the hypercharge run EEDKKRRER (one-letter aa code used).
The individual Archaea and Gram-positive sequences contain a corresponding significant mixed charge cluster in the location
of the charge cluster of the consensus sequence. In contrast, the four Gram-negative proteobacterial sequences of the alignment
do not have a charge cluster (even at the 5% significance level). All eukaryotic HSP70 sequences have the analogous charge
cluster. Strikingly, several of the eukaryotic isoforms show multiple mixed charged clusters. These clusters were interpreted
with supporting data related to HSP70 activity in facilitating chaperone, transport, and secretion function. We observed that
the consensus contains only a single tryptophan residue and a single conserved cysteine. This is interpreted with respect
to the target rule for disaggregating misfolded proteins. The mitochondrial HSP70 connections to bacterial HSP70 are analyzed,
suggesting a polyphyletic split of Trypanosoma and Leishmania protist mitochondrial (Mt) homologues separated from Mt-animal/fungal/plant homologues. Moreover, the HSP70 sequences from
the amitochondrial Entamoeba histolytica and Trichomonas vaginalis species were analyzed. The E. histolytica HSP70 is most similar to the higher eukaryotic cytoplasmic sequences, with significantly weaker alignments to ER sequences
and much diminished matching to all eubacterial, mitochondrial, and chloroplast sequences. This appears to be at variance
with the hypothesis that E. histolytica rather recently lost its mitochondrial organelle. T. vaginalis contains two HSP70 sequences, one Mt-like and the second similar to eukaryotic cytoplasmic sequences suggesting two diverse
origins.
Received: 29 January 1998 / Accepted: 14 May 1998 相似文献
14.
Vladimir V. Aleshin Irina A. Milyutina Olga S. Kedrova Natalia S. Vladychenskaya Nikolai B. Petrov 《Journal of molecular evolution》1998,47(5):597-605
Phylogenetic relationships of nematodes, nematomorphs, kinorhynchs, priapulids, and some other major groups of invertebrates
were studied by 18S rRNA gene sequencing. Kinorhynchs and priapulids form the monophyletic Cephalorhyncha clade that is the
closest to the coelomate animals. When phylogenetic trees were generated by different methods, the position of nematomorphs
appeared to be unstable. Inclusion of Enoplus brevis, a representative of a slowly evolving nematode lineage, in the set of analyzed species refutes the tree patterns, previously
derived from molecular data, where the nematodes appear as a basal bilateral lineage. The nematodes seem to be closer to the
coelomate animals than was speculated earlier. According to the results obtained, nematodes, nematomorphs, tardigrades, arthropods,
and cephalorhynchs are a paraphyletic association of closely related taxa.
Received: 1 December 1997 / Accepted: 9 April 1998 相似文献
15.
Singhania NA Dyer KD Zhang J Deming MS Bonville CA Domachowske JB Rosenberg HF 《Journal of molecular evolution》1999,49(6):721-728
The two eosinophil ribonucleases, eosinophil-derived neurotoxin (EDN/RNase 2) and eosinophil cationic protein (ECP/RNase
3), are among the most rapidly evolving coding sequences known among primates. The eight mouse genes identified as orthologs
of EDN and ECP form a highly divergent, species-limited cluster. We present here the rat ribonuclease cluster, a group of
eight distinct ribonuclease A superfamily genes that are more closely related to one another than they are to their murine
counterparts. The existence of independent gene clusters suggests that numerous duplications and diversification events have
occurred at these loci recently, sometime after the divergence of these two rodent species (∼10–15 million years ago). Nonsynonymous
substitutions per site (d
N) calculated for the 64 mouse/rat gene pairs indicate that these ribonucleases are incorporating nonsilent mutations at accelerated
rates, and comparisons of nonsynonymous to synonymous substitution (d
N / d
S) suggest that diversity in the mouse ribonuclease cluster is promoted by positive (Darwinian) selection. Although the pressures
promoting similar but clearly independent styles of rapid diversification among these primate and rodent genes remain uncertain,
our recent findings regarding the function of human EDN suggest a role for these ribonucleases in antiviral host defense.
Received: 8 April 1999 / Accepted: 22 June 1999 相似文献
16.
The large subunit ribosomal RNA sequences from the heterokont algae Ochromonas danica, Nannochloropsis salina, and Tribonema aequale were determined. These sequences were combined with small subunit ribosomal RNA sequences in order to carry out a phylogenetic
analysis based on neighbor-joining, maximum parsimony, and maximum likelihood methods. Our results indicate that heterokont
fungi and heterokont algae each are monophyletic, and confirm that they together form a monophyletic group called ``stramenopiles.'
Within the heterokont algae, the eustigmatophyte Nannochloropsis salina either clusters with the chrysophyte Ochromonas danica or forms a sister group to a cluster comprising the phaeophyte Scytosiphon lomentaria and the xanthophyte Tribonema aequale. The alveolates were identified as the closest relatives of the stramenopiles, but the exact order of divergence between the
eukaryotic crown taxa could not be established with confidence.
Received: 22 November 1996 / Accepted: 14 February 1997 相似文献
17.
Jean-Luc Desseyn Marie-Pierre Buisine Nicole Porchet Jean-Pierre Aubert Pierre Degand Anne Laine 《Journal of molecular evolution》1998,46(1):102-106
The four human mucin genes MUC6, MUC2, MUC5AC, and MUC5B are located at chromosome 11p15.5. It has been demonstrated that the three mucins MUC2, MUC5AC, and MUC5B contain several
Cys-subdomains of 108 amino acid residues. In contrast, little information is available concerning MUC6. These Cys-subdomains
contain 10 cysteine residues that have a highly conserved position. We present here a coherent probable evolutionary history
of this human gene family after comparison of the nucleotide sequences of these Cys-subdomains. The three MUC loci MUC2, MUC5AC, and MUC5B may have evolved from a common ancestral gene by two successive duplications. Moreover, we can postulate that MUC5AC and MUC5B have evolved in a concerted manner, while MUC2 has evolved separately.
Received: 30 January 1997 / Accepted: 17 April 1997 相似文献
18.
19.
Abdelaziz Heddi Hubert Charles Chaqué Khatchadourian Guy Bonnot Paul Nardon 《Journal of molecular evolution》1998,47(1):52-61
The principal intracellular symbiotic bacteria of the cereal weevil Sitophilus oryzae were characterized using the sequence of the 16S rDNA gene (rrs gene) and G + C content analysis. Polymerase chain reaction amplification with universal eubacterial primers of the rrs gene showed a single expected sequence of 1,501 bp. Comparison of this sequence with the available database sequences placed
the intracellular bacteria of S. oryzae as members of the Enterobacteriaceae family, closely related to the free-living bacteria, Erwinia herbicola and Escherichia coli, and the endocytobiotic bacteria of the tsetse fly and aphids. Moreover, by high-performance liquid chromatography, we measured
the genomic G + C content of the S. oryzae principal endocytobiotes (SOPE) as 54%, while the known genomic G + C content of most intracellular bacteria is about 39.5%.
Furthermore, based on the third codon position G + C content and the rrs gene G + C content, we demonstrated that most intracellular bacteria except SOPE are A + T biased irrespective of their phylogenetic
position. Finally, using the hsp60 gene sequence, the codon usage of SOPE was compared with that of two phylogenetically closely related bacteria: E. coli, a free-living bacterium, and Buchnera aphidicola, the intracellular symbiotic bacteria of aphids. Taken together, these results show a peculiar and distinctly different DNA
composition of SOPE with respect to the other obligate intracellular bacteria, and, combined with biological and biochemical
data, they elucidate the evolution of symbiosis in S. oryzae.
Received: 8 September 1997 / Accepted: 24 October 1997 相似文献
20.
Daniel R. Caffrey Luke A.J. O'Neill Denis C. Shields 《Journal of molecular evolution》1999,49(5):567-582
The MAP-kinase pathways are intracellular signaling modules that are likely to exist in all eukaryotes. We provide an evolutionary
model for these signaling pathways by focusing on the gene duplications that have occurred since the divergence of animals
from yeast. Construction of evolutionary trees with confidence assessed by bootstrap clearly shows that the mammalian JNK
and p38 pathways arose from an ancestral hyperosmolarity pathway after the split from yeast and before the split from C. elegans. These coduplications of interacting proteins at the MAPK and MEK levels have since evolved toward substrate specificity,
thus giving distinct pathways. Mammalian duplications since the split from C. elegans are often associated with divergent tissue distribution but do not appear to confer detectable substrate specificity. The
yeast kinase cascades have undergone similar fundamental functional changes since the split from mammals, with duplications
giving rise to central signaling components of the filamentous and hypoosmolarity pathways. Experimentally defined cross-talk
between yeast pheromone and hyperosmolarity pathways is mirrored with corresponding cross-talk in mammalian pathways, suggesting
the existence of ancient orthologous cross-talk; our analysis of gene duplications at all levels of the cascade is consistent
with this model but does not always provide significant bootstrap support. Our data also provide insights at different levels
of the cascade where conflicting experimental evidence exists.
Received: 2 December 1998 / Accepted: 9 June 1999 相似文献