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1.
Although molecular phylogenetic studies of cyanobacteria on the basis of the 16S rRNA gene sequence have been reported, the
topologies were unstable, especially in the inner branchings. Our analysis of 16S rRNA gene phylogeny by the maximum-likelihood
and neighbor-joining methods combined with rate homogeneous and heterogeneous models revealed seven major evolutionary lineages
of the cyanobacteria, including prochlorophycean organisms. These seven lineages are always stable on any combination of these
methods and models, fundamentally corresponding to phylogenetic relationships based on other genes, e.g., psbA, rbcL, rnpB, rpoC, and tufA. Moreover, although known genotypic and phenotypic characters sometimes appear paralleled in independent lineages, many characters
are not contradictory within each group. Therefore we propose seven evolutionary groups as a working hypothesis for successive
taxonomic reconstruction. New 16S rRNA sequences of five unicellular cyanobacterial strains, PCC 7001, PCC 7003, PCC 73109,
PCC 7117, and PCC 7335 of Synechococcus sp., were determined in this study. Although all these strains have been assigned to ``marine clusters B and C,' they were
separated into three lineages. This suggests that the organisms classified in the genus Synechococcus evolved diversely and should be reclassified in several independent taxonomic units. Moreover, Synechococcus strains and filamentous cyanobacteria make a monophyletic group supported by a comparatively high statistical confidence
value (80 to 100%) in each of the two independent lineages; therefore, these monophylies probably reflect the convergent evolution
of a multicellular organization.
Received: 3 September 1998 / Accepted: 30 November 1998 相似文献
2.
A number of proteins have been identified that contain prominent sequence signatures that are uniquely shared by the members
of the Deinococcus-Thermus genera and the cyanobacterial species but which are not found in any of the other eubacterial or archaebacterial homologs.
The proteins containing such sequence signatures include (1) the DnaJ/Hsp40 family of proteins, (2) DNA polymerase I, (3)
the protein synthesis elongation factor EF-Tu, and (4) the elongation factor EF-Ts. A strong affinity of the Deinococcus-Thermus species to cyanobacteria is also seen in the phylogenetic trees based on Hsp70 and DnaJ sequences. These results provide
strong evidence of a close and specific evolutionary relationship between species belonging to these two eubacterial divisions.
Received: 10 September 1997 / Accepted: 15 December 1997 相似文献
3.
Anton Karabinos Debashish Bhattacharya Hartmut D. Kratzin Norbert Hilschmann 《Journal of molecular evolution》1998,46(3):327-333
The human protein NEFA binds calcium, contains a leucine zipper repeat that does not form a homodimer, and is proposed (along
with the homologous Nuc protein) to have a common evolutionary history with an EF-hand ancestor. We have isolated and characterized
the N-terminal domain of NEFA that contains a signal sequence inferred from both endoproteinase Asp-N (Asp-N) and tryptic
digests. Analysis of this N-terminal sequence shows significant similarity to the conserved multiple domains of the mitochondrial
carrier family (MCF) proteins. The leader sequence of Nuc is, however, most similar to the signal sequences of membrane and/or
secreted proteins (e.g., mouse insulin-like growth factor receptor). We suggest that the divergent NEFA and Nuc N-terminal
sequences may have independent origins and that the common high hydrophobicity governs their targeting to the ER. These results
provide insights into signal sequence evolution and the multiple origins of protein targeting.
Received: 20 February 1997 / Accepted: 28 July 1997 相似文献
4.
Bujnicki JM 《Journal of molecular evolution》2000,50(1):39-44
To date all attempts to derive a phyletic relationship among restriction endonucleases (ENases) from multiple sequence alignments
have been limited by extreme divergence of these enzymes. Based on the approach of Johnson et al. (1990), I report for the
first time the evolutionary tree of the ENase-like protein superfamily inferred from quantitative comparison of atomic coordinates
of structurally characterized enzymes. The results presented are in harmony with previous comparisons obtained by crystallographic
analyses. It is shown that λ-exonuclease initially diverged from the common ancestor and then two ``endonucleolytic' families
branched out, separating ``blunt end cutters' from ``5′ four-base overhang cutters.' These data may contribute to a better
understanding of ENases and encourage the use of structure-based methods for inference of phylogenetic relationship among
extremely divergent proteins. In addition, the comparison of three-dimensional structures of ENase-like domains provides a
platform for further clustering analyses of sequence similarities among different branches of this large protein family, rational
choice of homology modeling templates, and targets for protein engineering.
Received: 14 June 1999 / Accepted: 11 August 1999 相似文献
5.
We analyzed the phylogenetic relationship between the species of Lordiphosa and other Drosophilidae using alcohol dehydrogenase (Adh) gene sequences. The phylogenetic trees consistently show that the four species Drosophila kurokawai, D. collinella, D. stackelbergi, and D. clarofinis, which include three species groups of Lordiphosa, form a monophyletic clade. This clade is placed as a sister group to the willistoni and saltans groups of Sophophora. On the other hand, three species of Lordiphosa, D. tenuicauda, D. pseudotenuicauda, and D. acutissima, all of which belong to the tenuicauda group, are not shown to be related to the major Lordiphosa lineage. In the phylogenetic trees, these species are included into the clade comprised of Drosophila and Hirtodrosophila, although it remains uncertain whether the tenuicauda group is a monophyletic group or not. These results indicate that Lordiphosa is polyphyletic and that most of the members of the subgenus have a close relationship to the neotropical groups of Sophophora. The above conclusion is compatible with the hypothesis of Okada (Mushi [1963] 37:79–100) and Lastovka and Máca (Acta Ent Bohemoslov [1978] 75:404–420) that Lordiphosa is most closely related to Sophophora; in contrast, our results contradict the hypothesis of Grimaldi (Bull Am Mus Nat Hist [1990] 197:1–139) that Lordiphosa is a sister group to the genus Scaptomyza.
Received: 12 May 1999 / Accepted: 14 April 2000 相似文献
6.
Piero Cammarano Roberta Creti Anna M. Sanangelantoni Peter Palm 《Journal of molecular evolution》1999,49(4):524-537
A global alignment of EF-G(2) sequences was corrected by reference to protein structure. The selection of characters eligible
for construction of phylogenetic trees was optimized by searching for regions arising from the artifactual matching of sequence
segments unique to different phylogenetic domains. The spurious matchings were identified by comparing all sections of the
global alignment with a comprehensive inventory of significant binary alignments obtained by BLAST probing of the DNA and
protein databases with representative EF-G(2) sequences. In three discrete alignment blocks (one in domain II and two in domain
IV), the alignment of the bacterial sequences with those of Archaea–Eucarya was not retrieved by database probing with EF-G(2)
sequences, and no EF-G homologue of the EF-2 sequence segments was detected by using partial EF-G(2) sequences as probes in
BLAST/FASTA searches. The two domain IV regions (one of which comprises the ADP-ribosylatable site of EF-2) are almost certainly
due to the artifactual alignment of insertion segments that are unique to Bacteria and to Archaea–Eucarya. Phylogenetic trees
have been constructed from the global alignment after deselecting positions encompassing the unretrieved, spuriously aligned
regions, as well as positions arising from misalignment of the G′ and G″ subdomain insertion segments flanking the ``fifth'
consensus motif of the G domain (?varsson, 1995). The results show inconsistencies between trees inferred by alternative methods
and alternative (DNA and protein) data sets with regard to Archaea being a monophyletic or paraphyletic grouping. Both maximum-likelihood
and maximum-parsimony methods do not allow discrimination (by log-likelihood difference and difference in number of inferred
substitutions) between the conflicting (monophyletic vs. paraphyletic Archaea) topologies. No specific EF-2 insertions (or
terminal accretions) supporting a crenarchaeal–eucaryal clade are detectable in the new EF-G(2) sequence alignment. 相似文献
7.
Yuji Inagaki Yasuko Hayashi-Ishimaru Megumi Ehara Ikuo Igarashi Takeshi Ohama 《Journal of molecular evolution》1997,45(3):295-300
The chloroplasts of euglenophytes and dinoflagellates have been suggested to be the vestiges of endosymbiotic algae acquired
during the process of evolution. However, the evolutionary positions of these organisms are still inconclusive, and they have
been tentatively classified as both algae and protozoa. A representative gene of the mitochondrial genome, cytochrome oxidase
subunit I (coxI), was chosen and sequenced to clarify the phylogenetic positions of four dinoflagellates, two euglenophytes and one apicomplexan
protist. This is the first report of mitochondrial DNA sequences for dinoflagellates and euglenophytes. Our COXI tree shows clearly that dinoflagellates are closely linked to apicomplexan parasites but not with algae. Euglenophytes and
algae appear to be only remotely related, with euglenophytes sharing a possible evolutionary link with kinetoplastids. The
COXI tree is in general agreement with the tree based on the nuclear encoded small subunit of ribosomal RNA (SSU rRNA) genes,
but conflicts with that based on plastid genes. These results support the interpretation that chloroplasts present in euglenophytes
and dinoflagellates were captured from algae through endosymbioses, while their mitochondria were inherited from the host
cell. We suggest that dinoflagellates and euglenophytes were originally heterotrophic protists and that their chloroplasts
are remnants of endosymbiotic algae.
Received: 24 March 1997 / Accepted: 21 April 1997 相似文献
8.
Molecular analyses have been used recently to refine our knowledge of phylogenetic relationships within the ciliated protozoa
(phylum Ciliophora). A current Hennigian phylogeny of the orders in the class Colpodea, based on light and electron microscopic
analyses, makes three important assumptions with regard to apomorphic character states, namely, (1) that the kreyellid silver
line evolved early in colpodean phylogeny, separating bryometopids, such as Bryometopus, from all other colpodeans; (2) that the macro–micronuclear complex is an autapomorphy of the cyrtolophosidids, such as Platyophrya; and (3) that merotelokinetal stomatogenesis is an apomorphic character of colpodids, such as Colpoda, Bresslaua, and Pseudoplatyophrya. These predictions of relationships within the class Colpodea were investigated by determining the complete small subunit
rRNA gene sequences for the colpodid Bresslaua vorax, the grossglockneriid Pseudoplatyophrya nana, and the cyrtolophosidid Platyophrya vorax and a partial sequence for the bryometopid Bryometopus sphagni. These sequences were combined with the previously published complete SSrRNA sequences for the colpodid Colpoda inflata and the bursariomorphid Bursaria truncatella. The affiliations were assessed using both distance matrix and maximum-parsimony analyses. The tree topologies for the class
Colpodea were identical in all analyses, with bootstrap support for bifurcations always exceeding 60%. The results suggest
the following. (1) Since the clade including Bryometopus and its sister taxon, Bursaria, is never basal, the kreyellid silver-line system evolved later in colpodean phylogeny and does not separate bryometopids
from all other colpodeans. (2) Since Platyophrya is always the sister taxon to the other five genera, there is a fundamental phylogenetic significance for its macro–micronuclear
complex. (3) Since the colpodids, Colpoda, Bresslaua, and Pseudoplatyophrya, always group in one clade, merotelokinetal stomatogenesis appears to be a derived character state.
Received: 30 June 1998 / Accepted: 3 December 1998 相似文献
9.
Phylogenetic relationships among the Japanese papilionid butterflies were analyzed by comparing 783 nucleotide sequences
of the mitochondrial gene encoding NADH dehydrogenase subunit 5 (ND5). Phylogenetic trees of the representative species from each family in the superfamily Papilionoidea revealed that the species
of the family Papilionidae and those of all other families formed distinct clusters, with a few species of the family Hesperiidae
(Hesperioidea) as an outgroup. In the phylogenetic trees of most Japanese species of the family Papilionidae with Nymphalis xanthomelas (Nymphalidae) as an outgroup, the tribe Parnassiini (Parnassiinae) formed a cluster, and the rest formed the other cluster
in which the tribe Zerynthiini (Parnassiinae) and the subfamily Papilioninae formed different subclusters. In the Papilioninae
cluster, the tribes Troidini and Graphiini formed a subcluster, and the tribe Papilionini formed the other subcluster. These
results generally agree with the traditional classification of the papilionid butterflies based on their morphological characteristics
and support the proposed evolutionary genealogy of the butterflies based on their morphology, behavior, and larval host plants,
except that the tribes Parnasiini and Zerynthiini (both Parnassiinae) are not in the same cluster.
Received: 16 March 1998 / Accepted: 28 April 1998 相似文献
10.
Tominaga O Su ZH Kim CG Okamoto M Imura Y Osawa S 《Journal of molecular evolution》2000,50(6):541-549
Phylogenetic analyses based on the mitochondrial ND5 gene comparisons and the geohistory of the Japanese Islands suggest
that each Japanese species belonging to the subtribe Carabina has its own history for the establishment of its present habitat
in the Japanese Islands. It can be roughly classified into two categories: (1) species which were derived from the ancestry
that inhabited ancient Japan at the time of its split from the Eurasian Continent [ca. 15 million years ago (MYA)], followed
by diversification within the Japanese Islands; and (2) species which invaded Hokkaido from the Eurasian Continent through
land-bridges from Sakhalin and/or the Kuriles or from western Japan from the Korean Peninsula during the glacial era (<2 MYA).
Received: 28 September 1999 / Accepted: 25 February 2000 相似文献
11.
The Origin of Chlorarachniophyte Plastids, as Inferred from Phylogenetic Comparisons of Amino Acid Sequences of EF-Tu 总被引:4,自引:0,他引:4
Ken-ichiro Ishida Ying Cao Masami Hasegawa Norihiro Okada Yoshiaki Hara 《Journal of molecular evolution》1997,45(6):682-687
A molecular phylogenetic analysis of elongation factor Tu (EF-Tu) proteins from plastids was performed in an attempt to identify
the origin of chlorarachniophyte plastids, which are considered to have evolved from the endosymbiont of a photosynthetic
eukaryote. Partial sequences of the genes for plastid EF-Tu proteins (1,080–1,089 bp) were determined for three algae that
contain chlorophyll b, namely, Gymnochlora stellata (Chlorarachniophyceae), Bryopsis maxima (Ulvophyceae), and Pyramimonas disomata (Prasinophyceae). The deduced amino acid sequences were used to construct phylogenetic trees of the plastid and bacterial
EF-Tu proteins by the maximum likelihood, the maximum parsimony, and the neighbor joining methods.
The trees obtained in the present analysis suggest that all plastids that contain chlorophyll b are monophyletic and that the chlorarachniophyte plastids are closely related to those of the Ulvophyceae. The phylogenetic
trees also suggest that euglenophyte plastids are closely related to prasinophycean plastids. The results indicate that the
chlorarachniophyte plastids evolved from a green algal endosymbiont that was closely related to the Ulvophyceae and that at
least two secondary endosymbiotic events have occurred in the lineage of algae with plastids that contain chlorophyll b.
Received: 10 March 1997 / Accepted: 28 July 1997 相似文献
12.
Freitas EM Gaudieri S Zhang WJ Kulski JK van Bockxmeer FM Christiansen FT Dawkins RL 《Journal of molecular evolution》2000,50(4):391-396
We have previously shown that several multicopy gene families within the major histocompatibility complex (MHC) arose from
a process of segmental duplication. It has also been observed that retroelements play a role in generating diversity within
these duplicated segments. The objective of this study was to compare the genomic organization of a gene duplication within
another multicopy gene family outside the MHC. Using new continuous genomic sequence encompassing the APOE-CII gene cluster,
we show that APOCI and its pseudogene, APOCI′, are contained within large duplicated segments which include sequences from
the hepatic control region (HCR). Flanking Alu sequences are observed at both ends of the duplicated unit, suggesting a possible
role in the integration of these segments. As observed previously within the MHC, the major differences between the segments
are the insertion of sequences (approximately 200–1000 bp in length), consisting predominantly of Alu sequences. Ancestral
retroelements also contribute to the generation of sequence diversity between the segments, especially within the 3′ poly(A)
tract of Alu sequences. The exonic and regulatory sequences of the APOCI and HCR loci show limited sequence diversity, with
exon 3 being an exception. Finally, the typing of pre- and postduplication Alus from both segments indicates an estimated
time of duplication of approximately 37 million years ago (mya), some time prior to the separation of Old and New World monkeys.
Received: 17 July 1999 / Accepted: 6 November 1999 相似文献
13.
In this paper we analyzed 49 lactate dehydrogenase (LDH) sequences, mostly from vertebrates. The amino acid sequence differences
were found to be larger for a human–killifish pair than a human–lamprey pair. This indicates that some protein sequence convergence
may occur and reduce the sequence differences in distantly related species. We also examined transitions and transversions
separately for several species pairs and found that the transitions tend to be saturated in the distantly related species
pair, while transversions are increasing. We conclude that transversions maintain a conservative rate through the evolutionary
time. Kimura's two-parameter model for multiple-hit correction on transversions only was used to derive a distance measure
and then construct a neighbor-joining (NJ) tree. Three findings were revealed from the NJ tree: (i) the branching order of
the tree is consistent with the common branch pattern of major vertebrates; (ii) Ldh-A and Ldh-B genes were duplicated near the origin of vertebrates; and (iii) Ldh-C and Ldh-A in mammals were produced by an independent gene duplication in early mammalian history. Furthermore, a relative rate test
showed that mammalian Ldh-C evolved more rapidly than mammalian Ldh-A. Under a two-rate model, this duplication event was calibrated to be approximately 247 million years ago (mya), dating back
to the Triassic period. Other gene duplication events were also discovered in Xenopus, the first duplication occurring approximately 60–70 mya in both Ldh-A and Ldh-B, followed by another recent gene duplication event, approximately 20 mya, in Ldh-B.
Received: 5 October 2001 / Accepted: 24 October 2001 相似文献
14.
Bocchetta M Gribaldo S Sanangelantoni A Cammarano P 《Journal of molecular evolution》2000,50(4):366-380
The phylogenetic placement of the Aquifex and Thermotoga lineages has been inferred from (i) the concatenated ribosomal proteins S10, L3, L4, L23, L2, S19, L22, and S3 encoded in
the S10 operon (833 aa positions); (ii) the joint sequences of the elongation factors Tu(1α) and G(2) coded by the str operon tuf and fus genes (733 aa positions); and (iii) the joint RNA polymerase β- and β′-type subunits encoded in the rpoBC operon (1130 aa positions). Phylogenies of r-protein and EF sequences support with moderate (r-proteins) to high statistical confidence (EFs) the placement of the two hyperthermophiles at the base of the bacterial clade
in agreement with phylogenies of rRNA sequences. In the more robust EF-based phylogenies, the branching of Aquifex and Thermotoga below the successive bacterial lineages is given at bootstrap proportions of 82% (maximum likelihood; ML) and 85% (maximum
parsimony; MP), in contrast to the trees inferred from the separate EF-Tu(1α) and EF-G(2) data sets, which lack both resolution
and statistical robustness. In the EF analysis MP outperforms ML in discriminating (at the 0.05 level) trees having A. pyrophilus and T. maritima as the most basal lineages from competing alternatives that have (i) mesophiles, or the Thermus genus, as the deepest bacterial radiation and (ii) a monophyletic A. pyrophilus–T. maritima cluster situated at the base of the bacterial clade. RNAP-based phylogenies are equivocal with respect to the Aquifex and Thermotoga placements. The two hyperthermophiles fall basal to all other bacterial phyla when potential artifacts contributed by the
compositionally biased and fast-evolving Mycoplasma genitalium and Mycoplasma pneumoniae sequences are eschewed. However, the branching order of the phyla is tenuously supported in ML trees inferred by the exhaustive
search method and is unresolved in ML trees inferred by the quartet puzzling algorithm. A rooting of the RNA polymerase-subunit
tree at the mycoplasma level seen in both the MP trees and the ML trees reconstructed with suboptimal amino acid substitution
models is not supported by the EF-based phylogenies which robustly affiliate mycoplasmas with low-G+C gram-positives and,
most probably, reflects a ``long branch attraction' artifact.
Received: 22 September 1999 / Accepted: 11 January 2000 相似文献
15.
Phylogenetic Relationships of Fungi, Plantae, and Animalia Inferred from Homologous Comparison of Ribosomal Proteins 总被引:6,自引:0,他引:6
The complete set of available ribosomal proteins was utilized, at both the peptidic and the nucleotidic level, to establish
that plants and metazoans form two sister clades relative to fungi. Different phylogenetic inference methods are applied to
the sequence data, using archeans as the outgroup. The evolutionary length of the internal branch within the eukaryotic crown
trichotomy is demonstrated to be, at most, one-tenth of the evolutionary length of the branch leading to the cenancester of
these three kingdoms.
Received: 1 November 1997 / Accepted: 7 January 1998 相似文献
16.
A 314-bp fragment of the mitochondrial 12S rRNA gene from 21 cestodes species of eight families was synthesized by PCR with
specially designed primers. These allowed amplification of parasite DNA without concomitant synthesis of host DNA. Phylogenetic
trees were inferred from the sequence data using three methods (maximum parsimony, maximum likelihood, and Fitch–Margoliash).
At the major nodes all three trees were similar. For the first time the genus Mesocestoides could be arranged into the Cyclophyllidea and a narrow relationship between the Mesocestoididae, Taeniidae, Hymenolepididae,
Anoplocephalidae, and Dipylidiidae was shown. Members of the families Catenotaeniidae and a cluster of two families (Hymenolepididae
and Dilepididae) form two monophyletic groups which derive prior to the remaining families of this phylogenetic study. A third
and a fourth clear monophyletic group were formed by the Taeniidae and by the Mesocestoididae. A high degree of variation
within the examined 304-bp fragment was observed between two isolates of Taenia taeniaeformis, supporting often discussed genetic heterogeneity within this species. In contrast, only one nucleotide exchange was found
in 23 isolates of Echinococcus multilocularis of various geographic origin, indicating that this species is genetically homogenous.
Received: 1 October 1997 / Accepted: 4 December 1997 相似文献
17.
We have isolated a 29,000-Da carbonic anhydrase (CA) protein from the zebrafish, Danio rerio, sequenced two peptide fragments, and tentatively identified it as a high-activity CA by inhibition kinetics. We have also
characterized a 1,537-bp message whose deduced sequence of 260 amino acids matches that of the isolated protein. This CA is
clearly an α-CA based on the similarity of its sequence to that of other members of the α-CA gene family. A phylogenetic analysis
suggested CAH-Z diverged after the branching of the CA-V and CA-VII genes and prior to the duplications that generated the
CA-I, CA-II, and CA-III genes of amniotes. This marks the first characterization of the mRNA and its protein product from
the CA gene of a teleost.
Received: 31 March 1996 / Accepted: 8 September 1996 相似文献
18.
Soullier S Jay P Poulat F Vanacker JM Berta P Laudet V 《Journal of molecular evolution》1999,48(5):517-527
From a database containing the published HMG protein sequences, we constructed an alignment of the HMG box functional domain
based on sequence identity. Due to the large number of sequences (more than 250) and the short size of this domain, several
data sets were used. This analysis reveals that the HMG box superfamily can be separated into two clearly defined subfamilies:
(i) the SOX/MATA/TCF family, which clusters proteins able to bind to specific DNA sequences; and (ii) the HMG/UBF family,
which clusters members which bind non specifically to DNA. The appearance and diversification of these subfamilies largely
predate the split between the yeast and the metazoan lineages. Particular emphasis was placed on the analysis of the SOX subfamily.
For the first time our analysis clearly identified the SOX subfamily as structured in six groups of genes named SOX5/6, SRY,
SOX2/3, SOX14, SOX4/22, and SOX9/18. The validity of these gene clusters is confirmed by their functional characteristics
and their sequences outside the HMG box. In sharp contrast, there are only a few robust branching patterns inside the UBF/HMG
family, probably because of the much more ancient diversification of this family than the diversification of the SOX family.
The only consistent groups that can be detected by our analysis are HMG box 1, vertebrate HMG box 2, insect SSRP, and plant
HMG. The various UBF boxes cannot be clustered together and their diversification appears to be extremely ancient, probably
before the appearance of metazoans.
Received: 20 July 1998 / Accepted: 19 October 1998 相似文献
19.
Sequence differences in the tRNA-proline (tRNApro) end of the mitochondrial control-region of three species of Pacific butterflyfishes accumulated 33–43 times more rapidly
than did changes within the mitochondrial cytochrome b gene (cytb). Rapid evolution in this region was accompanied by strong
transition/transversion bias and large variation in the probability of a DNA substitution among sites. These substitution
constraints placed an absolute ceiling on the magnitude of sequence divergence that could be detected between individuals.
This divergence ``ceiling' was reached rapidly and led to a decay in the relative rate of control-region/cytb b evolution.
A high rate of evolution in this section of the control-region of butterflyfishes stands in marked contrast to the patterns
reported in some other fish lineages. Although the mechanism underlying rate variation remains unclear, all taxa with rapid
evolution in the 5′-end of the control-region showed extreme transition biases. By contrast, in taxa with slower control-region
evolution, transitions accumulated at nearly the same rate as transversions. More information is needed to understand the
relationship between nucleotide bias and the rate of evolution in the 5′-end of the control-region.
Despite strong constraints on sequence change, phylogenetic information was preserved in the group of recently differentiated
species and supported the clustering of sequences into three major mtDNA groupings. Within these groups, very similar control-region
sequences were widely distributed across the Pacific Ocean and were shared between recognized species, indicating a lack of
mitochondrial sequence monophyly among species.
Received: 30 June 1996 / Accepted: 15 May 1997 相似文献
20.
Dynamic Diversification from a Putative Common Ancestor of Scorpion Toxins Affecting Sodium, Potassium, and Chloride Channels 总被引:11,自引:1,他引:10
Oren Froy Tal Sagiv Michal Poreh Daniel Urbach Noam Zilberberg Michael Gurevitz 《Journal of molecular evolution》1999,48(2):187-196
Scorpions have survived successfully over millions of years without detectable changes in their morphology. Instead, they
have developed an efficient alomonal machinery and a stinging device supporting their needs for prey and defense. They produce
a large variety of polypeptidic toxins that bind and modulate ion channel conductance in excitable tissues. The binding site,
mode of action, and chemical properties of many toxins have been studied extensively, but little is known about their genomic
organization and diversity. Genes representing each of the major classes of Buthidae scorpion toxins, namely, ``long' toxins,
affecting sodium channels (alpha, depressant, and excitatory), and ``short' toxins, affecting potassium and chloride channels,
were isolated from a single scorpion segment and analyzed. Each toxin type was found to be encoded by a gene family. Regardless
of toxin length, 3-D structure, and site of action, all genes contain A+T-rich introns that split, at a conserved location,
an amino acid codon of the signal sequence. The introns vary in length and sequence but display identical boundaries, agree
with the GT/AG splice junctions, and contain T-runs downstream of a putative branch point, 5′-TAAT-3′. Despite little sequence
similarity among all toxin classes, the conserved gene organization, intron features, and common cysteine-stabilized α-helical
(CSH) core connecting an α-helix to a three-stranded β-sheet suggest, that they all evolved from an ancestral common progenitor.
Furthermore, the vast diversity found among genomic copies, cDNAs, and their protein products for each toxin suggests an extensive
evolutionary process of the scorpion ``pharmaceutical factory,' whose success is due, most likely, to the inherent permissiveness
of the toxin exterior to structural alterations.
Received: 16 March 1998 / Accepted: 30 July 1998 相似文献