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1.
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
2.
A revised evolutionary history of hepatitis B virus (HBV) 总被引:8,自引:0,他引:8
Previous studies of the evolutionary history of hepatitis B virus (HBV) have been compromised by intergenotype recombination
and complex patterns of nucleotide substitution, perhaps caused by differential selection pressures. We examined the phylogenetic
distribution of recombination events among human HBV genotypes and found that genotypes A plus D, and genotypes B plus C,
had distinct patterns of recombination suggesting differing epidemiological relationships among them. By analyzing the nonoverlapping
regions of the viral genome we found strong bootstrap support for some intergenotypic groupings, with evidence of a division
between human genotypes A–E from the viruses sampled from apes and human genotype F. However, the earliest events in the divergence
of HBV remain uncertain. These uncertainties could not be explained by differential selection pressures, as the ratio of nonsynonymous-to-synonymous
substitutions (d
N/d
S) did not vary extensively among lineages and there is no strong evidence for positive selection across the whole tree. Finally,
we provide a new estimate of the mean substitution rate in HBV, 4.2 × 10−5, which suggests that divergence of HBV in humans and apes has occurred only in the last 6000 years. 相似文献
3.
Secondary structure is evaluated for determining evolutionary relationships between catalytic RNA molecules that are so distantly
related they are scarcely alignable. The ribonucleoproteins RNase P (P) and RNase MRP (MRP) have been suggested to be evolutionarily
related because of similarities in both function and secondary structure. However, their RNA sequences cannot be aligned with
any confidence, and this leads to uncertainty in any trees inferred from sequences. We report several approaches to using
secondary structures for inferring evolutionary trees and emphasize quantitative tests to demonstrate that evolutionary information
can be recovered. For P and MRP, three hypotheses for the relatedness are considered. The first is that MRP is derived from
P in early eukaryotes. The next is that MRP is derived from P from an early endosymbiont. The third is that both P and MRP
evolved in the RNA-world (and the need for MRP has since been lost in prokaryotes). Quantitative comparisons of the pRNA and
mrpRNA secondary structures have found that the possibility of an organellar origin of MRP is unlikely. In addition, comparison
of secondary structures support the identity of an RNase P–like sequence in the maize chloroplast genome. Overall, it is concluded
that RNA secondary structure is useful for evaluating evolutionary relatedness, even with sequences that cannot be aligned
with confidence.
Received: 19 July 1999 / Accepted: 3 May 2000 相似文献
4.
In this study we constructed a bootstrapped distance tree of 500 small subunit ribosomal RNA sequences from organisms belonging
to the so-called crown of eukaryote evolution. Taking into account the substitution rate of the individual nucleotides of
the rRNA sequence alignment, our results suggest that (1) animals, true fungi, and choanoflagellates share a common origin:
The branch joining these taxa is highly supported by bootstrap analysis (bootstrap support [BS] > 90%), (2) stramenopiles
and alveolates are sister groups (BS = 75%), (3) within the alveolates, dinoflagellates and apicomplexans share a common ancestor
BS > 95%), while in turn they both share a common origin with the ciliates (BS > 80%), and (4) within the stramenopiles, heterokont
algae, hyphochytriomycetes, and oomycetes form a monophyletic grouping well supported by bootstrap analysis (BS > 85%), preceded
by the well-supported successive divergence of labyrinthulomycetes and bicosoecids.
On the other hand, many evolutionary relationships between crown taxa are still obscure on the basis of 18S rRNA. The branching
order between the animal-fungal-choanoflagellates clade and the chlorobionts, the alveolates and stramenopiles, red algae,
and several smaller groups of organisms remains largely unresolved.
When among-site rate variation is not considered, the inferred tree topologies are inferior to those where the substitution
rate spectrum for the 18S rRNA is taken into account. This is primarily indicated by the erroneous branching of fast-evolving
sequences. Moreover, when different substitution rates among sites are not considered, the animals no longer appear as a monophyletic
grouping in most distance trees.
Received: 11 June 1997 / Accepted: 21 July 1997 相似文献
5.
Recent Evolutionary History of Human Immunodeficiency Virus Type 1 Subtype B: Reconstruction of Epidemic Onset Based on Sequence Distances to the Common Ancestor 总被引:13,自引:0,他引:13
We obtained and studied HIV-1 sequences with a known sampling year from three outbreaks of the HIV-1 epidemic: 141 env V3
(270 nt) sampled between 1984 and 1992 and 117 pol prot/RT (804 nt) sequences sampled between 1986 and 1999 from Dutch homosexual
men and injecting drug users (IDUs), as well as 77 env V3 sequences sampled between 1983 and 1994 in the United States. Since
retrospective serological and/or epidemiological data on these populations are available, providing estimates of the dates
of the onset of the HIV-1 epidemics, we had the opportunity to test different phylogenetic models for their accuracy in deriving
the recent evolutionary history of HIV-1 subtype B and the onset date of the HIV-1 epidemic. We observed that, in any given
year, individual sequences vary widely in their distances to the common ancestor, and sequences close to the ancestors were
found decades after the onset of the epidemic. Nevertheless, the mean evolutionary distances of virus strains to ancestors
were increasing significantly during the course of the studied epidemics, which indicates that the molecular clock is operational
in the recent evolution of HIV-1. When the relationship between the sampling years of sequences and their nucleotide distances
to the common ancestor was extrapolated to the past, analysis of pol sequences provided accurate estimates of the onset years
of the epidemics, whereas analysis of V3 sequences by the maximum-likelihood or neighbor-joining methods led to an overestimation
of the age of the epidemics. Separate analysis of nonsynonymous and synonymous distances revealed that this overestimation
results from nonsynonymous substitutions, whose numbers were not increasing significantly in all three virus populations over
the observation period. In contrast, analysis of synonymous env V3 distances provided accurate estimates of the onset years
for the outbreaks we studied.
Received: 26 October 2001 / Accepted: 8 November 2001 相似文献
6.
To characterize the coding-sequence divergence of closely related genomes, we compared DNA sequence divergence between sequences
from a Brassica rapa ssp. pekinensis EST library isolated from flower buds and genomic sequences from Arabidopsis thaliana. The specific objectives were (i) to determine the distribution of and relationship between K
a and K
s, (ii) to identify genes with the lowest and highest K
a:K
s values, and (iii) to evaluate how codon usage has diverged between two closely related species. We found that the distribution
of K
a:K
s was unimodal, and that substitution rates were more variable at nonsynonymous than synonymous sites, and detected no evidence
that K
a and K
s were positively correlated. Several genes had K
a:K
s values equal to or near zero, as expected for genes that have evolved under strong selective constraint. In contrast, there
were no genes with K
a:K
s >1 and thus we found no strong evidence that any of the 218 sequences we analyzed have evolved in response to positive selection.
We detected a stronger codon bias but a lower frequency of GC at synonymous sites in A. thaliana than B. rapa. Moreover, there has been a shift in the profile of most commonly used synonymous codons since these two species diverged
from one another. This shift in codon usage may have been caused by stronger selection acting on codon usage or by a shift
in the direction of mutational bias in the B. rapa phylogenetic lineage. 相似文献
7.
Thomas J.S. Merritt Siana LaForest Glenn D. Prestwich Joseph M. Quattro Richard G. Vogt 《Journal of molecular evolution》1998,46(3):272-276
We have isolated and characterized cDNAs representing two distinct pheromone binding proteins (PBPs) from the gypsy moth,
Lymantria dispar. We use the L. dispar protein sequences, along with other published lepidopteran PBPs, to investigate the evolutionary relationships among genes
within the PBP multigene family. Our analyses suggest that the presence of two distinct PBPs in genera representing separate
moth superfamilies is the result of relatively recent, independent, gene duplication events rather than a single, ancient,
duplication. We discuss this result with respect to the biochemical diversification of moth PBPs.
Received: 19 March 1997 / Accepted: 11 July 1997 相似文献
8.
Hong Xue 《Journal of molecular evolution》1998,47(3):323-333
The gene superfamily of ligand-gated ion channel (LGIC) receptors is composed of members of excitatory LGIC receptors (ELGIC)
and inhibitory LGIC receptors (ILGIC), all using amino acids as ligands. The ILGICs, including GABAA, Gly, and GluCl receptors, conduct Cl− when the ligand is bound. To evaluate the phylogenetic relationships among ILGIC members, 90 protein sequences were analyzed
by both maximum-parsimony and distance matrix-based methods. The strength of the resulting phylogenetic trees was evaluated
by means of bootstrap. Four major phylogenetic branches are recognized. Branch I, called BZ, for the majority of the members
are known to be related to benzodiazepine binding, is subdivided into IA, composed of all GABAA receptor α subunits, and IB, composed of the γ and ε subunits, which are shown to be tightly linked. Branch II, named NB
for non–benzodiazepine binding, and consisting of GABAA receptor β, δ, π, and ρ subunits, is further subdivided into IIA, containing β subunits; IIB, containing δ, and π subunits;
and IIC, containing ρ subunits. Branch IIIA, composed of vertebrate Gly receptors, is loosely clustered with Branch IIIB,
composed of invertebrate GluCl receptors, to form Branch III, which is designated NA for being non–GABA responsive. Branch
IV is called UD for being undefined in specificity. The existence of primitive forms of GABAA receptor non-β subunits in invertebrates is first suggested by the present analysis, and the identities of sequences p25123
from Drosophila melanogaster, s34469 from Lymnaea stagnalis, and u14635 and p41849 from C. aenorhabditis elegans are determined to be different from their previously given annotations. The proposed branching classification of ILGICs provides
a phylogenetic map, based on protein sequences, for tracing the evolutionary pathways of ILGIC receptor subunits and determining
the identities of newly discovered subunits on the basis of their protein sequences.
Received: 15 April 1997 / Accepted: 11 March 1998 相似文献
9.
A.A. Paszek G.H. Flickinger L. Fontanesi C.W. Beattie G.A. Rohrer L. Alexander L.B. Schook 《Journal of molecular evolution》1998,46(1):121-126
We report the use of microsatellites (MS) to track the recent evolution of swine. Allelic frequencies for nine MS loci linked
on swine chromosome 6 (SSC6) representing four western and one Chinese swine breeds were used to estimate genetic distances
and times of breed divergence. A phylogenetic tree was constructed which partitioned into western and Meishan breed branches.
Yorkshire and Hampshire breeds exhibited the most recent divergence with a calculated distance of 391 years. The oldest divergence,
of 2,227 years, was between Meishan and Hampshire swine. Estimates of breed divergence are consistent with historical records.
Additional analysis suggests that polymorphic MS linked on a single chromosome are sufficient to determine evolutionary relationships
within a single species.
Received: 23 September 1996 / Accepted: 26 April 1997 相似文献
10.
Three types of electrical excitation have been investigated in the marine diatom Coscinodiscus wailesii. I: Depolarization-triggered, transient Cl− conductance, G
Cl
(t), followed by a transient, voltage-gated K+ conductance, G
K
, with an active state a and two inactive states i
1 and i
2 in series (a-i
1-i
2). II: Similar G
Cl
(t) as in Type-I but triggered by hyperpolarization; a subsequent increase of G
K
in this type is indicated but not analyzed in detail. III: Hyperpolarization-induced transient of a voltage-gated activity
of an electrogenic pump (i
2-a-i
2), followed by G
Cl
(t) as in Type-II excitations. Type-III with pump gating is novel as such. G
Cl
(t) in all types seems to reflect the mechanism of InsP−
3 and Ca2+-mediated G
Cl
(t) in the action potential in Chara (Biskup et al., 1999). The nonlinear current-voltage-time relationships of Type-I and Type-III excitations have been recorded
under voltage-clamp using single saw-tooth command voltages (voltage range: −200 to +50 mV, typical slope: ±1 Vs−1). Fits of the corresponding models to the experimental data provided numerical values of the model parameters. The statistical
significance of these solutions is investigated. We suggest that the original function of electrical excitability of biological
membranes is related to osmoregulation which has persisted through evolution in plants, whereas the familiar and osmotically
neutral action potentials in animals have evolved later towards the novel function of rapid transmission of information over
long distances.
Received: 2 December 1999/Revised: 3 March 2000 相似文献
11.
The amino acid sequences of 22 α-amylases from family 13 of glycosyl hydrolases were analyzed with the aim of revealing the
evolutionary relationships between the archaeal α-amylases and their eubacterial and eukaryotic counterparts. Two evolutionary
distance trees were constructed: (i) the first one based on the alignment of extracted best-conserved sequence regions (58
residues) comprising β2, β3, β4, β5, β7, and β8 strand segments of the catalytic (α/β)8-barrel and a short conserved stretch in domain B protruding out of the barrel in the β3 →α3 loop, and (ii) the second one
based on the alignment of the substantial continuous part of the (α/β)8-barrel involving the entire domain B (consensus length: 386 residues). With regard to archaeal α-amylases, both trees compared
brought, in fact, the same results; i.e., all family 13 α-amylases from domain Archaea were clustered with barley pI isozymes,
which represent all plant α-amylases. The enzymes from Bacillus licheniformis and Escherichia coli, representing liquefying and cytoplasmic α-amylases, respectively, seem to be the further closest relatives to archaeal α-amylases.
This evolutionary relatedness clearly reflects the discussed similarities in the amino acid sequences of these α-amylases,
especially in the best-conserved sequence regions. Since the results for α-amylases belonging to all three domains (Eucarya,
Eubacteria, Archaea) offered by both evolutionary trees are very similar, it is proposed that the investigated conserved sequence
regions may indeed constitute the ``sequence fingerprints' of a given α-amylase.
Received: 3 June 1998 / Accepted: 20 August 1998 相似文献
12.
Elena SF Dopazo J de la Peña M Flores R Diener TO Moya A 《Journal of molecular evolution》2001,53(2):155-159
The proposed monophyletic origin of a group of subviral plant pathogens (viroids and viroid-like satellite RNAs), as well
as the phylogenetic relationships and the resulting taxonomy of these entities, has been recently questioned. The criticism
comes from the (apparent) lack of sequence similarity among these RNAs necessary to reliably infer a phylogeny. Here we show
that, despite their low overall sequence similarity, a sequence alignment manually adjusted to take into account all the local
similarities and the insertions/deletions and duplications/rearrangements described in the literature for viroids and viroid-like
satellite RNA, along with the use of an appropriate estimator of genetic distances, constitutes a data set suitable for a
phylogenetic reconstruction. When the likelihood-mapping method was applied to this data set, the tree-likeness obtained was
higher than that corresponding to a sequence alignment that does not take into consideration the local similarities. In addition,
bootstrap analysis also supports the major groups previously proposed and the reconstruction is consistent with the biological
properties of this RNAs.
Received: 17 January 2001 / Accepted: 16 March 2001 相似文献
13.
James R. Brown Frank T. Robb Robert Weiss W. Ford Doolittle 《Journal of molecular evolution》1997,45(1):9-16
Each amino acid is attached to its cognate tRNA by a distinct aminoacyl-tRNA synthetase (aaRS). The conventional evolutionary
view is that the modern complement of synthetases existed prior to the divergence of eubacteria and eukaryotes. Thus comparisons
of prokaryotic and eukaryotic aminoacyl-tRNA synthetases of the same type (charging specificity) should show greater sequence
similarities than comparisons between synthetases of different types—and this is almost always so. However, a recent study
[Ribas de Pouplana L, Furgier M, Quinn CL, Schimmel P (1996) Proc Natl Acad Sci USA 93:166–170] suggested that tryptophanyl- (TrpRS) and tyrosyl-tRNA (TyrRS) synthetases of the Eucarya (eukaryotes) are more
similar to each other than either is to counterparts in the Bacteria (eubacteria). Here, we reexamine the evolutionary relationships
of TyrRS and TrpRS using a broader range of taxa, including new sequence data from the Archaea (archaebacteria) as well as
species of Eucarya and Bacteria. Our results differ from those of Ribas de Pouplana et al.: All phylogenetic methods support
the separate monophyly of TrpRS and TyrRS. We attribute this result to the inclusion of the archaeal data which might serve
to reduce long branch effects possibly associated with eukaryotic TrpRS and TyrRS sequences. Furthermore, reciprocally rooted
phylogenies of TrpRS and TyrRS sequences confirm the closer evolutionary relationship of Archaea to eukaryotes by placing
the root of the universal tree in the Bacteria.
Received: 7 December 1996 / Accepted: 11 February 1997 相似文献
14.
Van Mau N Missé D Le Grimellec C Divita G Heitz F Veas F 《The Journal of membrane biology》2000,177(3):251-257
Increasing evidence suggests that the HIV envelope binds through its surface (SU) gp120 not only to receptors and coreceptors,
but also to other components of the cellular membrane where the glycolipids appear to be good candidates. To assess the ability
of HIV-1 SU gp120 to penetrate into phospholipid membranes, we carried out a study of the interactions between a recombinant
SU gp120 from HIV-1/HXB2 and artificial lipid monolayers mimicking the composition of the outer leaflet of the lymphocytes
and which were spread at the air-water interface. We show that the protein, in its aggregated form, has amphipathic properties
and that the insertion of this amphipathic species into lipids is favored by the presence of sphingomyelin. Furthermore, cholesterol
enhances the penetration into mixed phosphatidylcholine-sphingomyelin monolayers. Coexistence of different physical states
of the lipids and thus of domains appears to play a major role for protein penetration independently of the presence of receptors
and coreceptors.
Received: 24 April 2000/Revised: 11 July 2000 相似文献
15.
The recent completion of the sequencing of the Saccharomyces cerevisiae genome provides a unique opportunity to analyze the evolutionary relationships existing among the entire complement of retrotransposons
residing within a single genome. In this article we report the results of such an analysis of two closely related families
of yeast long terminal repeat (LTR) retrotransposons, Ty1 and Ty2. In our study, we analyzed the molecular variation existing
among the 32 Ty1 and 13 Ty2 elements present within the S. cerevisiae genome recently sequenced within the context of the yeast genome project. Our results indicate that while the Ty1 family
is most likely ancestral to Ty2 elements, both families of elements are relatively recent components of the S. cerevisiae genome. Our results also indicate that both families of elements have been subject to purifying selection within their protein
coding regions. Finally, and perhaps most interestingly, our results indicate that a relatively recent recombination event
has occurred between Ty2 and a subclass of Ty1 elements involving the LTR regulatory region. We discuss the possible biological
significance of these findings and, in particular, how they contribute to a better overall understanding of LTR retrotransposon
evolution.
Received: 30 September 1997 / Accepted: 3 February 1998 相似文献
16.
Molecular evolution of a portion of the mitochondrial 16S ribosomal gene region in scleractinian corals 总被引:1,自引:0,他引:1
Relationships among families and suborders of scleractinian corals are poorly understood because of difficulties 1) in making
inferences about the evolution of the morphological characters used in coral taxonomy and 2) in interpreting their 240-million-year
fossil record. Here we describe patterns of molecular evolution in a segment of the mitochondrial (mt) 16S ribosomal gene from taxa of 14 families of corals and the use of this gene segment in a phylogenetic analysis of relationships
within the order. We show that sequences obtained from scleractinians are homologous to other metazoan 16S ribosomal sequences
and fall into two distinct clades defined by size of the amplified gene product. Comparisons of sequences from the two clades
demonstrate that both sets of sequences are evolving under similar evolutionary constraints: they do not differ in nucleotide
composition, numbers of transition and transversion substitutions, spatial patterns of substitutions, or in rates of divergence.
The characteristics and patterns observed in these sequences as well as the secondary structures, are similar to those observed
in mt 16S ribosomal DNA sequences from other taxa. Phylogenetic analysis of these sequences shows that they are useful for evaluating
relationships within the order. The hypothesis generated from this analysis differs from traditional hypotheses for evolutionary
relationships among the Scleractinia and suggests that a reevaluation of evolutionary affinities in the order is needed.
Received: 4 September 1996 / Accepted: 7 April 1997 相似文献
17.
We have expressed recombinant α-subunits of hH1 (human heart subtype 1), rSkM1 (rat skeletal muscle subtype 1) and hSkM1 (human
skeletal muscle) sodium channels in human embryonic kidney cell line, namely the tsA201 cells and compared the effects of
ATX II on these sodium channel subtypes. ATX II slows the inactivation phase of hH1 with little or no effect on activation.
At intermediate concentrations of ATX II the time course of inactivation is biexponential due to the mixture of free (fast
component, τfast
h
) and toxin-bound (slow component, τslow
h
) channels. The relative amplitude of τslow
h
allows an estimate of the IC50 values ∼11 nm. The slowing of inactivation in the presence of ATX II is consistent with destabilization of the inactivated state by toxin
binding. Further evidence for this conclusion is: (i) The voltage-dependence of the current decay time constants (τ
h
) is lost or possibly reversed (time constants plateau or increase at more positive voltages in contrast to these of untreated
channels). (ii) The single channel mean open times are increased by a factor of two in the presence of ATX II. (iii) The recovery
from inactivation is faster in the presence of ATX II.
Similar effects of ATX II on rSkM1 channel behavior occur, but only at higher concentrations of toxin (IC50= 51 nm). The slowing of inactivation on hSkM1 is comparable to the one seen with rSkM1.
A residual or window current appears in the presence of ATX II that is similar to that observed in channels containing mutations
associated with some of the familial periodic paralyses.
Received: 5 December 1995/Revised: 1 March 1996 相似文献
18.
B. S. Stamova R. T. Chetelat 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,101(4):527-537
Cucumber mosaic virus (CMV) infects a wide variety of crop plants and in tomato (Lycopersicon esculentum Mill.) causes significant economic losses in many growing regions, particularly the Mediterranean. The objective of the present
study was to identify the number and map locations of genes controlling resistance to CMV in breeding lines (BC1–inbreds) derived from the related wild species L. chilense. These lines also carried the gene Tm-2
a
for resistance to ToMV, which facilitated the interpretation of disease symptoms. The segregation for CMV resistance in the
BC2F1 and BC2F2 generations, following mechanical inoculation with subgroup-I isolates, was consistent with expectations for a single dominant
gene, for which the symbol Cmr (cucumber mosaic resistance) was given. Resistant and susceptible BC1-inbreds were analyzed with RFLP and isozyme markers to identify genomic regions introgressed from L. chilense. The only L. chilense-specific markers found were on chromosome 12; some resistant lines contained a single introgression comprising the entire
short arm and part of the long arm of this chromosome, while others contained a recombinant derivative of this introgression.
The chromosome 12 markers were significantly associated with CMV resistance in both qualitative and quantitative models of
inheritance. The qualitative analysis, however, demonstrated that CMV resistance was not expressed as a reliable monogenic
character, suggesting a lack of penetrance, significant environmental effects, or the existence of additional (undetected)
resistance factors. In the quantitative analysis, the marker interval TG68 – CT79 showed the most significant association
with CMV resistance. No association between CMV resistance and the Tm-2
a
gene was observed. These breeding lines are potentially useful sources of CMV resistance for tomato improvement, in which
context knowledge of the map location of Cmr should accelerate introgression by marker-assisted selection.
Received: 9 August 1999 / Accepted: 22 December 1999 相似文献
19.
Recombination is well known as a complicating factor in the interpretation of molecular phylogenies. Here we describe a maximum
likelihood sliding window method based on a likelihood ratio test for scanning DNA sequence alignments for regions of incongruent
phylogenetic signals, such as those influenced by recombination. Using this method, we identify several instances of gene
conversion between paralogous chaperonin genes in euryarchaeote Archaea, many of which are not detected by two other widely
used methods. In the Thermococcus/Pyrococcus lineage, where a gene duplication producing a and b paralogues predates the divergence of Thermococcus strains KS-1 and KS-8, gene conversion has homogenized portions of the a and b genes in KS-8 since the divergence of these two strains. A region near the 3′ end of the a and b paralogues in the methanogen Methanobacterium thermoautotrophicum also appears to have undergone gene conversion. We apply the method to two additional test data sets, the argF gene of Neisseria and a set of actin paralogues in maize, and show that it successfully identifies all the recombinant regions that were previously
detected with other methods. Our approach is relatively insensitive to the presence of divergent sequences in the alignment,
making it ideal for detecting recombination between both closely and distantly related genes. 相似文献
20.
To determine the origin and evolutionary significance of a recently discovered isoform of the estrogen receptor (ERβ), we
examined the phylogenetic relationship of ERβ to the well-known α isoform (ERα) and other steroid receptors. Our phylogenetic
analyses traced the origin of ERβ to a single duplication event at least 450 million years ago. Since this duplication, the
evolution of both ER isoforms has apparently been constrained such that 80% of the amino acid positions in the DNA binding
domain (DBD) and 53% of the ligand binding domain (LBD) have remained unchanged. Using the phylogenetic tree, we determined
the amount of evolutionary change that had occurred in two ER isoforms. The DBD and the LBD had lower rates of evolutionary
change compared to the NH2 terminal domain. However, even with strong selective constraints on the DBD and LBD, our phylogenetic analyses demonstrate
two clearly separate phylogenetic histories for ERα and ERβ dating back several hundred million years. The ancient duplication
of ER and the parallel evolution of the two ER isoforms suggest that, although ERα and ERβ share a substantial degree of sequence
identity, they play unique roles in vertebrate physiology and reproduction.
Received: 19 January 1999 / Accepted: 26 May 1999 相似文献