共查询到20条相似文献,搜索用时 15 毫秒
1.
Glutamine synthetase type I (GSI) genes have previously been described only in prokaryotes except that the fungus Emericella nidulans contains a gene (fluG) which encodes a protein with a large N-terminal domain linked to a C-terminal GSI-like domain. Eukaryotes generally contain
the type II (GSII) genes which have been shown to occur also in some prokaryotes. The question of whether GSI and GSII genes
are orthologues or paralogues remains a point of controversy. In this article we show that GSI-like genes are widespread in
higher plants and have characterized one of the genes from the legume Medicago truncatula. This gene is part of a small gene family and is expressed in many organs of the plant. It encodes a protein similar in size
and with between 36 and 46% amino acid sequence similarity to prokaryotic GS proteins used in the analyses, whereas it is
larger and with less than 25% similarity to GSII proteins, including those from the same plant species. Phylogenetic analyses
suggest that this protein is most similar to putative proteins encoded by expressed sequence tags of other higher plant species
(including dicots and a monocot) and forms a cluster with FluG as the most divergent of the GSI sequences. The discovery of
GSI-like genes in higher plants supports the paralogous evolution of GSI and GSII genes, which has implications for the use
of GS in molecular studies on evolution.
Received: 4 May 1999 / Accepted: 17 September 1999 相似文献
2.
Short Inverted-Repeat Transposable Elements in Teleost Fish and Implications for a Mechanism of Their Amplification 总被引:7,自引:0,他引:7
Zsuzsanna Izsvák Zoltán Ivics Nobuyoshi Shimoda Deanna Mohn Hitoshi Okamoto Perry B. Hackett 《Journal of molecular evolution》1999,48(1):13-21
Angel is the first miniature inverted-repeat transposable element (MITE) isolated from fish. Angel elements are imperfect palindromes with the potential to form stem-loop structures in vitro. Despite sequence divergence
of elements of up to 55% within and between species, their inverted repeat structures have been maintained, implying functional
importance. We estimate that there are about 103–104
Angels scattered throughout the zebrafish genome, evidence that this family of transposable elements has been significantly amplified
over the course of evolution. Angel elements and Xenopus MITEs carry common sequence motifs at their termini, indicating common origin and/or related mechanisms of transposition.
We present a model in which MITEs take advantage of the basic cellular mechanism of DNA replication for their amplification,
which is dependent on the characteristic inverted repeat structures of these elements. We propose that MITEs are genomic parasites
that transpose via a DNA intermediate, which forms by a folding-back of a single strand of DNA, that borrow all of the necessary
factors for their amplification from products encoded in the genomes in which they reside. DNA polymorphisms in different
lines of zebrafish were detected by PCR using Angel-specific primers, indicating that such elements, combined with other transposons in vertebrate genomes, will be useful molecular
tools for genome mapping and genetic analyses of mutations.
Received: 7 April 1998 / Accepted: 7 April 1998 相似文献
3.
Synonymous Codon Choices in the Extremely GC-Poor Genome of Plasmodium falciparum: Compositional Constraints and Translational Selection 总被引:7,自引:0,他引:7
Héctor Musto Héctor Romero Alejandro Zavala Kamel Jabbari Giorgio Bernardi 《Journal of molecular evolution》1999,49(1):27-35
We have analyzed the patterns of synonymous codon preferences of the nuclear genes of Plasmodium falciparum, a unicellular parasite characterized by an extremely GC-poor genome. When all genes are considered, codon usage is strongly
biased toward A and T in third codon positions, as expected, but multivariate statistical analysis detects a major trend among
genes. At one end genes display codon choices determined mainly by the extreme genome composition of this parasite, and very
probably their expression level is low. At the other end a few genes exhibit an increased relative usage of a particular subset
of codons, many of which are C-ending. Since the majority of these few genes is putatively highly expressed, we postulate
that the increased C-ending codons are translationally optimal. In conclusion, while codon usage of the majority of P. falciparum genes is determined mainly by compositional constraints, a small number of genes exhibit translational selection.
Received: 10 November 1998 / Accepted: 28 January 1999 相似文献
4.
Zelus D Robinson-Rechavi M Delacre M Auriault C Laudet V 《Journal of molecular evolution》2000,51(3):234-244
Interleukin-2 (IL-2) is a cytokine involved in induction and regulation of the immune response in mammals. There have been
numerous reports about the search for IL-2 in species other than mammals, and recently an IL-2-like gene has been isolated
in chicken. Using PCR, we searched for IL-2 gene sequences in a wide variety of mammals, including marsupials and monotremes,
as well as in birds. Although we can readily amplify IL-2 gene fragments in placental mammals, no amplification was obtained
in other species. This is best explained by very high substitution rates. This suggest that strategies to isolate IL-2 homologous
genes outside mammals should involve functional assays, as for the chicken gene, and not hybridization-based techniques. Nonsynonymous
substitution rates are especially high in ruminants, due to positive selection acting on regions important in term of structure-function.
We suggest that, although globally similar, the immune response of various mammals is not identical, mainly at the level of
cytokine-mediated regulations.
Received: 27 July 1999 / Accepted: 15 April 2000 相似文献
5.
M.E. Forero M. Marín A. Corrales I. Llano H. Moreno M. Camacho 《The Journal of membrane biology》1999,170(2):173-180
Whole cell patch-clamp recordings were used to study the electrical properties of the macrophage-like cell line J774.1, after
infection with Leishmania amazonensis. Infection induced a significant increase in cell size and membrane capacitance, suggesting that parasite invasion leads to
the addition of plasma membrane to the host cell. By 24 hr after infection, the host cell membrane potential was significantly
more hyperpolarized than control cells, and this difference remained for the subsequent 72 hr post-infection. The hyperpolarization
was paralleled by an increase in the density of inward rectifying K+ currents. The shape of the conductance vs. voltage curve, the kinetic properties and the pharmacological profile of these currents were not significantly altered by
infection. These results suggest that infection by L. amazonensis causes an increase in the number of functional inward rectifying K+ channels, leading to hyperpolarization of the host cell membrane.
Received: 19 January 1999/Revised: 20 April 1999 相似文献
6.
Weinreich DM 《Journal of molecular evolution》2001,52(1):40-50
A higher rate of molecular evolution in rodents than in primates at synonymous sites and, to a lesser extent, at amino acid
replacement sites has been reported previously for most nuclear genes examined. Thus in these genes the average ratio of amino
acid replacement to synonymous substitution rates in rodents is lower than in primates, an observation at odds with the neutral
model of molecular evolution. Under Ohta's mildly deleterious model of molecular evolution, these observations are seen as
the consequence of the combined effects of a shorter generation time (driving a higher mutation rate) and a larger effective
population size (resulting in more effective selection against mildly deleterious mutations) in rodents. The present study
reports the results of a maximum-likelihood analysis of the ratio of amino acid replacements to synonymous substitutions for
genes encoded in mitochondrial DNA (mtDNA) in these two lineages. A similar pattern is observed: in rodents this ratio is
significantly lower than in primates, again consistent only with the mildly deleterious model. Interestingly the lineage-specific
difference is much more pronounced in mtDNA-encoded than in nuclear-encoded proteins, an observation which is shown to run
counter to expectation under Ohta's model. Finally, accepting certain fossil divergence dates, the lineage-specific difference
in amino acid replacement-to-synonymous substitution ratio in mtDNA can be partitioned and is found to be entirely the consequence
of a higher mutation rate in rodents. This conclusion is consistent with a replication-dependent model of mutation in mtDNA.
Received: 24 September 1999 / Accepted: 18 September 2000 相似文献
7.
Genetic Variability of Natural Populations of Cotton Leaf Curl Geminivirus, a Single-Stranded DNA Virus 总被引:5,自引:0,他引:5
Ana I. Sanz Aurora Fraile Jesus M. Gallego Jose M. Malpica Fernando García-Arenal 《Journal of molecular evolution》1999,49(5):672-681
Reports on the genetic variability and evolution of natural populations of DNA viruses are scarce in comparison with the
abundant information on the variability of RNA viruses. Geminiviruses are plant viruses with circular ssDNA genomes that are
replicated by the host plant DNA polymerases. Whitefly-transmitted geminiviruses (WTG) are the agents of important diseases
of crop plants and best exemplify emerging plant viruses. In this report we have analyzed the genetic diversity of cotton
leaf curl geminivirus (CLCuV), a typical emerging WTG. No genetic differentiation was observed between isolates from different
host plant species or geographic regions. Thus, the analyzed isolates represented a unique, undifferentiated population. Genetic
variability, estimated as nucleotide diversities at synonymous positions in open reading frames (ORFs) for the AC1 (=replication)
protein and coat protein (CP = AV1), was very high, exceeding the values reported for different genes in several plant and
animal RNA viruses. This was unexpected in a virus that uses the DNA replication machinery of its eukaryotic host. Diversities
at nonsynonymous positions, on the other hand, indicated that variability may be constrained in the genome of CLCuV. The ratio
of nonsynonymous-to-synonymous substitutions varied for the different ORFs: they were higher for CP than for AC1 and lower
still for the AC4 and AV2 ORFs, which overlap AC1 and CP ORFs, respectively. Analysis of nucleotide diversities at synonymous
and nonsynonymous positions of the AC4 and AV2 ORFs suggest that their evolution is constrained by AC1 and CP, respectively.
Data suggest that AC4 and AV2 are new genes that may have originated by overprinting on the preexistent AC1 and CP genes.
Evidence for recombination was found for the AC1 and CP ORFs and for the noncoding intergenic region (IR). Data indicate that
the origin of replication is a major recombination point in the IR, but not the only one. Analyses of the IR also suggest
that recombinants may be frequent in the population and that recombination may have an important role in the generation of
CLCuV variability.
Received: 26 February 1999 / Accepted: 31 May 1999 相似文献
8.
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
9.
Peeters NM Chapron A Giritch A Grandjean O Lancelin D Lhomme T Vivrel A Small I 《Journal of molecular evolution》2000,50(5):413-423
Two cysteinyl-tRNA synthetases (CysRS) and four asparaginyl-tRNA synthetases (AsnRS) from Arabidopsis thaliana were characterized from genome sequence data, EST sequences, and RACE sequences. For one CysRS and one AsnRS, sequence alignments
and prediction programs suggested the presence of an N-terminal organellar targeting peptide. Transient expression of these
putative targeting sequences joined to jellyfish green fluorescent protein (GFP) demonstrated that both presequences can efficiently
dual-target GFP to mitochondria and plastids. The other CysRS and AsnRSs lack targeting sequences and presumably aminoacylate
cytosolic tRNAs. Phylogenetic analysis suggests that the four AsnRSs evolved by repeated duplication of a gene transferred
from an ancestral plastid and that the CysRSs also arose by duplication of a transferred organelle gene (possibly mitochondrial).
These case histories are the best examples to date of capture of organellar aminoacyl-tRNA synthetases by the cytosolic protein
synthesis machinery.
Received: 8 October 1999 / Accepted: 23 January 2000 相似文献
10.
Alexander E. Vinogradov 《Journal of molecular evolution》1999,49(3):376-384
The intron–genome size relationship was studied across a wide evolutionary range (from slime mold and yeast to human and
maize), as well as the relationship between genome size and the ratio of intervening/coding sequence size. The average intron
size is scaled to genome size with a slope of about one-fourth for the log-transformed values; i.e., on the global scale its
increase in evolution is lower than the increase in genome size by four orders of magnitude. There are exceptions to the general
trend. In baker's yeast introns are extraordinarily long for its genome size. Tetrapods also have longer introns than expected
for their genome sizes. In teleost fish the mean intron size does not differ significantly, notwithstanding the differences
in genome size. In contrast to previous reports, avian introns were not found to be significantly shorter than introns of
mammals, although avian genomes are smaller than genomes of mammals on average by about a factor of 2.5. The extra-/intragenic
ratio of noncoding DNA can be higher in fungi than in animals, notwithstanding the smaller fungal genomes. In vertebrates
and invertebrates taken separately, this ratio is increasing as the increase in genome size. Two hypotheses are proposed to
explain the variation in the extra-/intragenic ratio of noncoding DNA in organisms with similar numbers of genes: transition
(dynamic) and equilibrium (static). According to the transition model, this variation arises with the rapid shift of genome
size because the bulk of extragenic DNA can be changed more rapidly than the finely interspersed intron sequences. The equilibrium
model assumes that this variation is a result of selective adjustment of genome size with constraints imposed on the intron
size due to its putative link to chromatin structure (and constraints of the splicing machinery).
Received: 23 October 1997 / Accepted: 14 April 1999 相似文献
11.
The Nonrandom Location of Synonymous Codons Suggests That Reading Frame-Independent Forces Have Patterned Codon Preferences 总被引:6,自引:0,他引:6
Biased codon usage is common in eukaryotic and prokaryotic genes. Evidence from Escherichia, Saccharomyces, and Drosophila indicates that it favors translational efficiency and accuracy. However, to date no functional advantages have been identified
in the codon–anticodon interactions involving the most frequently used (preferred) codons. Here we present evidence that forces
not related to the individual codon–anticodon interaction may be involved in determining which synonymous codons are preferred
or avoided. We show that the ``off-frame' trinucleotide motif preferences inferrable from Drosophila coding regions are often in the same direction as Drosophila's ``in-frame' codon preferences, i.e., its codon usage. The off-frame preferences were inferred from the nonrandomness of
the location of confamilial synonymous codons along coding regions—a pattern often described as a context dependence of nucleotide
choice at synonymous positions or as codon-pair bias. We relied on randomizations of the location of confamilial codons that
do not alter, and cannot be influenced by, the encoded amino acid sequences, codon usage, or base composition of the genes
examined. The statistically significant congruency of in-frame and off-frame trinucleotide preferences suggests that the same
kind of reading-frame-independent force(s) may also influence synonymous codon choice. These forces may have produced biases
in codon usage that then led to the evolution of the translational advantages of these motifs as preferred codons. Under this
scenario, tRNA pool size differences between preferred and nonpreferred codons initially were evolved to track the default
overrepresentation of codons with preferred motifs. The motif preference hypothesis can explain the structuring of codon preferences
and the similarities in the codon usages of distantly related organisms.
Received: 10 November 1998 / Accepted: 23 February 1999 相似文献
12.
To determine whether the persistent nature of hepatitis C infection is related to the emergence of antigenic variants driven
by immune selection, we examined the sequence heterogeneity in a portion of the hepatitis C virus (HCV) nonstructural 3 (NS3)
gene of a patient infected over the course of more than 2 years. By PCR amplification, cloning, and sequencing, we observed
several variable and conserved regions in the NS3 segment of the HCV genome. All variable regions had higher ratios of nonsynonymous/synonymous
mutations and encompassed immunodominant epitopes, and their locations were not essential to maintain the known function of
HCV RNA helicase. In contrast, the regions that are critical for HCV RNA helicase activity were found to be conserved with
lower heterogeneity or lower ratios of nonsynonymous/synonymous mutations, and none except one of these regions was encoded
within immunodominant epitopes. Our results are consistent with immune selection of viral variants at the epitope and molecular
levels that may enable HCV to evade host defenses over time. Plotting the relatedness of sequence variants revealed a star
topology suggesting that a wild-type HCV sequence is maintained, unlike HIV.
Received: 2 November 2000 / Accepted: 1 October 2001 相似文献
13.
We examined the evolution of the repeat regions of three noncoding microsatellite loci in 58 species of the Polistinae, a
subfamily of wasps that diverged over 140 million years ago. A phylogenetic approach allows two new kinds of approaches to
studying microsatellite evolution: character mapping and comparative analysis. The basic repeat structure of the loci was
highly conserved, but was often punctuated with imperfections that appear to be phylogenetically informative. Repeat numbers
evolved more rapidly than other changes in the repeat region. Changes in number of repeats among species seem consistent with
the stepwise mutation model, which is based on slippage during replication as the main source of mutations. Changes in repeat
numbers can occur even when there are very few tandem repeats but longer repeats, especially perfect repeats led to greater
rates of evolutionary change. Species phylogenetically closer to the one from which we identified the loci had longer stretches
of uninterrupted repeats and more different motifs, but not longer total repeat regions. The number of perfect repeats increased
more often than it decreased. However, there was no evidence that some species have consistently greater numbers of repeats
across loci than other species have, once ascertainment bias is eliminated. We also found no evidence for a population size
effect posited by one form of the directionality hypothesis. Overall, phylogenetic variation in repeat regions can be explained
by adding neutral evolution to what is already known about the mutation process. The life cycle of microsatellites appears
to reflect a balance between growth by slippage and degradation by an essentially irreversible accumulation of imperfections.
Received: 13 April 1999 / Accepted: 8 September 1999 相似文献
14.
We combined widely different biochemical methods to analyze proteins of the cell surface of P. tetraurelia since so far one can isolate only a subfraction of cell membrane vesicles enriched in the GPI-anchored surface antigens (``immoblization'
or ``i-AGs'). We also found that i-AGs may undergo partial degradation by endogenous proteases. Genuine intrinsic membrane
proteins were recognized particularly with lipophilic 5-[125I]-iodonaphthalene-1-azide (INA) labeling which reportedly ``sees' integral proteins and cytoplasmic cell membrane-associated
proteins. With INA (+DTT), bands of ≤55 kDa were similar as with hydrophilic iodogen (+DTT), but instead of large size bands
including i-AGs, a group of 122, 104 and 94 kDa appeared. Several bands of the non i-AG type are compatible with integral
(possibly oligomeric) or associated proteins of the cell membrane of established molecular identity, as we discuss. In summary,
we can discriminate between i-AGs and some functionally important minor cell membrane components. Our methodical approach
might be relevant also for an analysis of some related protozoan parasites.
Received: 5 April 1999/Revised: 19 July 1999 相似文献
15.
Amino acid residues arginine (R) and lysine (K) have similar physicochemical characteristics and are often mutually substituted
during evolution without affecting protein function. Statistical examinations on human proteins show that more R than K residues
are used in the proximity of R residues, whereas more K than R are used near K residues. This biased use occurs on both a
global and a local scale (shorter than ∼100 residues). Even within a given exon, G + C-rich and A + T-rich short DNA segments
preferentially encode R and K, respectively. The biased use of R and K on a local scale is also seen in Saccharomyces cerevisiae and Caenorhabdidtis elegans, which lack global-scale mosaic structures with varying GC%, or isochores. Besides R and K, several amino acids are also used
with a positive or negative correlation with the local GC% of third codon bases. The local-, or ``within-gene'-, scale heterogeneity
of the DNA sequence may influence the sequence of the encoded protein segment.
Received: 2 March 1998 / Accepted: 23 April 1998 相似文献
16.
If lateral gene transfer (LGT) has affected all genes over the course of prokaryotic evolution, reconstruction of organismal
phylogeny is compromised. However, if a core of genes is immune to transfer, then the evolutionary history of that core might
be our most reliable guide to the evolution of organisms. Such a core should be preferentially included in the subset of genes
shared by all organisms, but where universally conserved genes have been analyzed, there is too little phylogenetic signal
to allow determination of whether or not they indeed have the same history (Hansmann and Martin 2000; Teichmann and Mitchison
1999). Here we look at a more restricted set, 521 homologous genes (COGs) simultaneously present in four sequenced euryarchaeal
genomes. Although there is overall little robust phylogenetic signal in this data set, there is, among well-supported trees,
strong representation of all three possible four-taxon topologies. ``Informational' genes seem no less subject to LGT than
are ``operational genes,' within the euryarchaeotes. We conclude that (i) even in this collection of conserved genes there
has been extensive LGT (orthologous gene replacement) and (ii) the notion that there is a core of nontransferable genes (the
``core hypothesis') has not been proven and may be unprovable.
Received: 7 November 2000 / Accepted: 20 February 2001 相似文献
17.
RNA viruses and retroviruses fix substitutions approximately 1 million-fold faster than their hosts. This diversification
could represent an inevitable drift under purifying selection, the majority of substitutions being phenotypically neutral.
The alternative is to suppose that most fixed mutations are beneficial to the virus, allowing it to keep ahead of the host
and/or host population. Here, relative sequence diversification of different proteins encoded by viral genomes is found to
be linear. The examples encompass a wide variety of retroviruses and RNA viruses. The smoothness of relative divergence spans
quasispeciation following clonal infection, to variation among different isolates of the same virus, to viruses from different
species or those associated with different diseases, indicating that the majority of fixed mutations likely reflects drift.
This held for both mammalian and plant viruses, indicating that adaptive immunity doesn't necessarily shape the relative accumulation
of amino acid substitutions. When compared to their hosts RNA viruses evolution appears conservative.
Received: 16 November 1999 / Accepted: 10 March 2000 相似文献
18.
Michael S.Y. Lee 《Journal of molecular evolution》1999,49(3):385-391
It has recently been argued that living metazoans diverged over 800 million years ago, based on evidence from 22 nuclear
genes for such a deep divergence between vertebrates and arthropods (Gu 1998). Two ``internal' calibration points were used.
However, only one fossil divergence date (the mammal–bird split) was directly used to calibrate the molecular clock. The second
calibration point (the primate–rodent split) was based on molecular estimates that were ultimately also calibrated by the
same mammal–bird split. However, the first tetrapods that can be assigned with confidence to either the mammal (synapsid)
lineage or the bird (diapsid) lineage are approximately 288 million years old, while the first mammals that can be assigned
with confidence to either the primate or the rodent lineages are 65 million years old, or 85 million years old if ferungulates
are part of the primate lineage and zhelestids are accepted as ferungulate relatives. Recalibration of the protein data using
these fossil dates indicates that metazoans diverged between 791 and 528 million years ago, a result broadly consistent with
the palaeontological documentation of the ``Cambrian explosion.' The third, ``external' calibration point (the metazoan–fungal
divergence) was similarly problematic, since it was based on a controversial molecular study (which in turn used fossil dates
including the mammal–bird split); direct use of fossils for this calibration point gives the absurd dating of 455 million
years for metazoan divergences. Similar calibration problems affect another recent study (Wang et al. 1999), which proposes
divergences for metazoans of 1000 million years or more: recalibrations of their clock again yields much more recent dates,
some consistent with a ``Cambrian explosion' scenario. Molecular clock studies have persuasively argued for the imperfection
of the fossil record but have rarely acknowledged that their inferences are also directly based on this same record.
Received: 26 January 1999 / Accepted: 14 April 1999 相似文献
19.
David Posada 《Journal of molecular evolution》2001,52(5):434-444
Models of sequence evolution play an important role in molecular evolutionary studies. The use of inappropriate models of
evolution may bias the results of the analysis and lead to erroneous conclusions. Several procedures for selecting the best-fit
model of evolution for the data at hand have been proposed, like the likelihood ratio test (LRT) and the Akaike (AIC) and
Bayesian (BIC) information criteria. The relative performance of these model-selecting algorithms has not yet been studied
under a range of different model trees. In this study, the influence of branch length variation upon model selection is characterized.
This is done by simulating sequence alignments under a known model of nucleotide substitution, and recording how often this
true model is recovered by different model-fitting strategies. Results of this study agree with previous simulations and suggest
that model selection is reasonably accurate. However, different model selection methods showed distinct levels of accuracy.
Some LRT approaches showed better performance than the AIC or BIC information criteria. Within the LRTs, model selection is
affected by the complexity of the initial model selected for the comparisons, and only slightly by the order in which different
parameters are added to the model. A specific hierarchy of LRTs, which starts from a simple model of evolution, performed
overall better than other possible LRT hierarchies, or than the AIC or BIC.
Received: 2 October 2000 / Accepted: 4 January 2001 相似文献
20.
M. Mar Albà Mauro F. Santibáñez-Koref John M. Hancock 《Journal of molecular evolution》2001,52(3):249-259
Polyglutamine repeats within proteins are common in eukaryotes and are associated with neurological diseases in humans. Many
are encoded by tandem repeats of the codon CAG that are likely to mutate primarily by replication slippage. However, a recent
study in the yeast Saccharomyces cerevisiae has indicated that many others are encoded by mixtures of CAG and CAA which are less likely to undergo slippage. Here we
attempt to estimate the proportions of polyglutamine repeats encoded by slippage-prone structures in species currently the
subject of genome sequencing projects. We find a general excess over random expectation of polyglutamine repeats encoded by
tandem repeats of codons. We nevertheless find many repeats encoded by nontandem codon structures. Mammals and Drosophila display extreme opposite patterns. Drosophila contains many proteins with polyglutamine tracts but these are generally encoded by interrupted structures. These structures
may have been selected to be resistant to slippage. In contrast, mammals (humans and mice) have a high proportion of proteins
in which repeats are encoded by tandem codon structures. In humans, these include most of the triplet expansion disease genes.
Received: 17 August 2000 / Accepted: 20 November 2000 相似文献