共查询到20条相似文献,搜索用时 484 毫秒
1.
Nucleotide Composition Bias Affects Amino Acid Content in Proteins Coded by Animal Mitochondria 总被引:16,自引:0,他引:16
We show that in animal mitochondria homologous genes that differ in guanine plus cytosine (G + C) content code for proteins
differing in amino acid content in a manner that relates to the G + C content of the codons. DNA sequences were analyzed using
square plots, a new method that combines graphical visualization and statistical analysis of compositional differences in
both DNA and protein. Square plots divide codons into four groups based on first and second position A + T (adenine plus thymine)
and G + C content and indicate differences in amino acid content when comparing sequences that differ in G + C content. When
sequences are compared using these plots, the amino acid content is shown to correlate with the nucleotide bias of the genes.
This amino acid effect is shown in all protein-coding genes in the mitochondrial genome, including cox I, cox II, and cyt b, mitochondrial genes which are commonly used for phylogenetic studies. Furthermore, nucleotide content differences are shown
to affect the content of all amino acids with A + T- and G + C-rich codons. We speculate that phylogenetic analysis of genes
so affected may tend erroneously to indicate relatedness (or lack thereof) based only on amino acid content.
Received: 3 July 1996 / Accepted: 6 November 1996 相似文献
2.
Maximum likelihood (ML) phylogenies based on 9,957 amino acid (AA) sites of 45 proteins encoded in the plastid genomes of
Cyanophora, a diatom, a rhodophyte (red algae), a euglenophyte, and five land plants are compared with respect to several properties
of the data, including between-site rate variation and aberrant amino acid composition in individual species. Neighbor-joining
trees from AA LogDet distances and ML analyses are seen to be congruent when site rate variability was taken into account.
Four feasible trees are identified in these analyses, one of which is preferred, and one of which is almost excluded by statistical
criteria. A transition probability matrix for the general reversible Markov model of amino acid substitutions is estimated
from the data, assuming each of these four trees. In all cases, the tree with diatom and rhodophyte as sister taxa was clearly
favored. The new transition matrix based on the best tree, called cpREV, takes into account distinct substitution patterns
in plastid-encoded proteins and should be useful in future ML inferences using such data. A second rate matrix, called cpREV*,
based on a weighted sum of rate matrices from different trees, is also considered.
Received: 3 June 1999 / Accepted: 26 November 1999 相似文献
3.
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
4.
Jan Kwiatowski Michal Krawczyk Michal Jaworski Douglas Skarecky F.J. Ayala 《Journal of molecular evolution》1997,44(1):9-22
We have studied the evolution of Gpdh in 18 fruitfly species by sequencing 1,077 nucleotides per species on average. The region sequenced includes four exons coding
for 277 amino acids and three variable-length introns. Phylogenies derived by a variety of methods confirm that the nominal
genus Zaprionus belongs within the genus Drosophila, whereas Scaptodrosophila and Chymomyza are outside. The rate of GPDH evolution is erratic. The rate of amino acid replacements in a lineage appears to be 1.0 ×
10−10/site/year when Drosophila species are considered (diverged up to 55 million years ago), but becomes 2.3 × 10−10 when they are compared to Chymomyza species (divergence around 60 My ago), and 4.6 × 10−10 when species of those two genera are compared with the medfly Ceratitis capitata (divergence around 100 My ago). In order to account for these observations, the rate of amino acid replacement must have
been 15 or more times greater in some lineages and at some times than in others. At the nucleotide level, however, Gpdh evolves in a fairly clockwise fashion.
Received: 13 June 1996 / Accepted: 16 August 1996 相似文献
5.
Five cDNAs (pDidact2–pDidact6), representing different actin genes, were isolated from a Diphyllobothrium dendriticum cDNA library, and the DNA as well as the putative amino acid sequences were determined. The corresponding Didact2 and Didact4 genes code for peptides 376 amino acids long, with molecular weights 41,772 and 41,744 Da, respectively, while the deduced
Didact3 protein is 377 amino acids long and weighs 41,912 Da. The pDidact5 and -6 cDNAs lack nucleotides corresponding to three to six amino acids at the amino-terminus. Two of the five cDNAs contain the
conventional AATAAA as the putative polyadenylation signal, one has the common variant ATTAAA, whereas the hexanucleotide
AATAGA is found 15 and 18 nucleotides, respectively, upstream of the poly(A) site in two of the cDNAs. Phylogenetic studies
including 102 actin protein sequences revealed that there are at least four different types of cestode actins. In this study
three of these types were found to be expressed in the adult D. dendriticum tapeworm. Structurally the cestode actin groupings differ from each other to an extent seen only among the metazoan actins
between the vertebrate muscle and cytoplasmic isoforms. In the phylogenetic trees constructed, cestode actins were seen to
map to two different regions, one on the border of the metazoan actins and the other within this group. It is, however, difficult
to say whether the cestode actins branched off early in the metazoan evolution or if this position in the phylogenetic tree
only reflects upon differences in evolutionary rate.
Received: 19 June 1996 / Accepted: 20 August 1996 相似文献
6.
The genus Chrysolina consists of specialized phytophagous leaf-beetles (Coleoptera, Chrysomelidae) with feed on several plant families. There
is no explicit phylogenetic hypothesis available for this genus, which includes 65 subgenera and more than 400 species with
a wide distribution. We obtained 839-bp sequence data from the 16S rDNA and cytochrome oxidase subunit I (COI) mitochondrial
genes. Thirty Chrysolina taxa representing eight host–plant affiliations, two species of the closely related genus Oreina, and two outgroups were sampled. These data sets were used separately and combined to obtain the mitochondrial cladogram of
the group using maximum-parsimony and maximum-likelihood criteria. The results were compared to current proposals for Chrysolina systematics that are based on morphological, ecological, and karyological data. The trees obtained were in the most part
congruent with the proposed ancestral association of Chrysolina to Lamiaceae based on chromosome number in several lineages. A minimum of five host-plant switches from the ancestral state
inferred at the family level and two at the subclass level suggests the absence of parallel evolution of beetles and their
host plants. Another switch leading to oligophagy at the family level was deduced to have occurred in the lineage of the subgenus
Chrysolina s.str.
Received: 22 May 1998 / Accepted: 16 September 1998 相似文献
7.
The aminoacyl-tRNA synthetases are ubiquitous enzymes which catalyze a crucial step of the cell life, the specific attachment
of amino acids to their cognate tRNA. The amino acid sequences of three archaeal seryl-tRNA synthetases (SerRS) from Haloarcula marismortui and Methanococcus jannaschii, both belonging to the group of Euryarchaeota, and from Sulfolobus solfataricus, of the group of Crenarchaeota, were aligned with other eubacterial and eukaryal available SerRS sequences. In an attempt to identify some features of adaptation
to extreme environments of these organisms, amino acid composition and amino acid substitutions between mesophilic and thermophilic
SerRS were analyzed. In addition, universal phylogenetic trees of SerRS including the three known archaeal sequences, rooted
by the threonyl-tRNA synthetases were inferred. Amino acid analyses of the SerRS revealed two ways of adaptation to thermophilic
environments between the Eubacteria and the Archaea; most of the usually described amino acid substitutions were nonsignificant in the case of archaeal thermophilic SerRS and
most amino acid composition biases seemed to be linked to the genome G+C content pressure. The phylogenetic analysis of the
SerRS showed the Archaea to be paraphyletic, H. marismortui emerging with the Gram-positive Bacteria, M. jannaschii being near the root of the tree, and S. solfataricus branching with Eucarya.
Received: 30 March 1998 / Accepted: 14 July 1998 相似文献
8.
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
9.
Mitochondrial DNA (mtDNA) sequences are widely used for inferring the phylogenetic relationships among species. Clearly,
the assumed model of nucleotide or amino acid substitution used should be as realistic as possible. Dependence among neighboring
nucleotides in a codon complicates modeling of nucleotide substitutions in protein-encoding genes. It seems preferable to
model amino acid substitution rather than nucleotide substitution. Therefore, we present a transition probability matrix of
the general reversible Markov model of amino acid substitution for mtDNA-encoded proteins. The matrix is estimated by the
maximum likelihood (ML) method from the complete sequence data of mtDNA from 20 vertebrate species. This matrix represents
the substitution pattern of the mtDNA-encoded proteins and shows some differences from the matrix estimated from the nuclear-encoded
proteins. The use of this matrix would be recommended in inferring trees from mtDNA-encoded protein sequences by the ML method.
Received: 3 May 1995 / Accepted: 31 October 1995 相似文献
10.
Niji Ohta Naoki Sato Hisayoshi Nozaki Tsuneyoshi Kuroiwa 《Journal of molecular evolution》1997,45(6):688-695
The nucleotide sequence of a cluster of ribosomal protein genes in the plastid genome of a unicellular red alga, Cyanidioschyzon merolae, which has been supposed to be the most primitive alga, was determined. The phylogenetic tree inferred from the amino acid
sequence of ribosomal proteins of two rhodophytes, a chromophyte, a glaucophyte, two chlorophytes (land plants), a cyanobacterium,
and three eubacteria suggested a close relationship between the cyanobacterium Synechocystis PCC6803 and the plastids of various species in the kingdom Plantae, which is consistent with the hypothesis of the endosymbiotic
origin of plastids. In this tree, the two species of rhodophytes were grouped with the chromophyte, and the glaucophyte was
grouped with the chlorophytes. Analysis of the organization of the genes encoding the ribosomal proteins suggested that the
translocation of the str cluster occurred early in the lineage of rhodophytes and chromophytes after these groups had been separated from chlorophytes
and glaucophytes.
Received: 2 June 1997 / Accepted: 15 July 1997 相似文献
11.
Kiyoto Maekawa Masahiro Kon Kunio Araya Tadao Matsumoto 《Journal of molecular evolution》2001,53(6):651-659
Molecular phylogenetic relationships among 25 species of the wood-feeding cockroach belonging to the genus Salganea St?l (Panesthiinae; Blaberidae) in Southeast Asia were analyzed based on the DNA sequence of the complete mitochondrial cytochrome
oxidase II (COII) gene. Most basal relationships among species of Salganea are poorly resolved by both neighbor-joining and nonweighted parsimony analyses, suggesting the possibility of a hard polytomy
due to a rapid and potentially simultaneous radiation early in the history of the genus. For more apical relationships, however,
some interesting phylogenetic relationships were recognized. The monophyly of the two species groups, morio and foveolata, the former of which is distributed mainly in the Sunda lands (containing the Malay Peninsula, Sumatra, Java, and Borneo),
whereas the latter is Sulawesi endemic, was strongly supported. Based on the inferred phylogenetic patterns and recent palaeogeographic
scenario for Southeast Asia, it is suggested that a radiation of Salganea species occurred in Southeast Asia presumably in the early Tertiary, and several barriers against dispersal and gene flow,
such as the formation of straits or high mountains, have arisen from the middle Tertiary.
Received: 4 April 2001 / Accepted: 20 April 2001 相似文献
12.
The usage of synonymous codons and the frequencies of amino acids were investigated in the complete genome of the bacterium
Thermotoga maritima using a multivariate statistical approach. The GC3 content of each gene was the most prominent source of variation of codon
usage. Surprisingly the usage of UGU and UGC (synonymous triplets coding for Cys, the least frequent amino acid in this species)
was detected as the second most prominent source of variation. However, this result is probably an artifact due to the very
low frequency of Cys together with the nonbiased composition of this genome. The third trend was related to the preferential
usage of a subset of codons among highly expressed genes, and these triplets are presumed to be translationally optimal. Concerning
the amino acid usage, the hydropathy level of each protein (and therefore the frequency of charged residues) was the main
trend, while the second factor was related to the frequency of usage of the smaller residues, suggesting that the cell economy
strongly influences the architecture of the proteins. The third axis of the analysis discriminated the usage of Phe, Tyr,
Trp (aromatic residues) plus Cys, Met, and His. These six residues have in common the property of being the preferential targets
of reactive oxygen species, and therefore the anaerobic condition of T. maritima is an important factor for the amino acid frequencies. Finally, the Cys content of each protein was the fourth trend.
Received: 22 June 2001 / Accepted: 1 October 2001 相似文献
13.
We have examined the evolution of a gene, SM50, encoding a component of the spicule matrix, which plays an integral role
in the formation of the echinoderm skeleton. This gene was originally characterized in Strongylocentrotus purpuratus and encodes an imperfect tandem repeat of six or seven amino acids. We have analyzed the sequence of this repeat in a number
of sea urchin species and have determined that the repeat regions have undergone concerted evolution. There are differences
in the repeat region between species, but the overall repeat structure is conserved, suggesting the repeat forms a structural
domain important in biomineralization. The inherent conserved amino acid repeat structure promotes concerted evolution due
to the high probability of misreplication and unequal crossing-over in the repeated segment of the gene. While there are constraints
on the amino acids allowed in the repeat region, there are also variations, so that the sequences observed illustrate the
balance between amino acid substitutions and concerted evolution. We have evidence that substitutions can alter the mechanisms
of unequal crossing-over, altering the way concerted evolution occurs. The way in which concerted evolution occurred appears
to be determined by the degree of sequence similarity between the repeats in a given gene, which influences how unequal crossing
over may occur. We have mapped the differences in repeat regions on existing phylogenetic trees and indicate where concerted
evolution has taken place. We also confirm an earlier report that Hemicentrotus pulcherrimus fits into the Strongylocentrotus genus and examine the evolution of the H. pulcherrimus SM50 repeat relative to other members of this genus.
Received: 31 October 2000 / Accepted: 20 March 2001 相似文献
14.
The mammalian defensin molecule is a short, highly cationic peptide cytotoxic to both microbial and mammalian cells which
is cleaved from a precursor including a signal peptide and a highly anionic propiece. A phylogenetic analysis of 28 complete
sequences from five mammalian species (mouse, rat, guinea pig, rabbit, and human) showed species-specific clusters of sequences,
indicating that the genes duplicated after divergence of these species. Comparison of rates of synonymous and nonsynonymous
nucleotide substitution suggested that gene duplication has often been followed by a period in which diversification of the
mature defensins at the amino acid level has been selectively favored. In some comparisons, it appeared that amino acid differences
in this region have appeared in a nonrandom fashion so as to change the pattern of residue charges. Because it has been hypothesized
that the negative charge in the propiece serves to balance the positive charge in the mature defensin and thus to prevent
cytotoxicity prior to cleavage, we used a maximum likelihood method of reconstructing ancestral states in order to test whether
this balance has been maintained over evolutionary time in spite of rapid diversification of the mature defensin at the amino
acid level. Reconstructed ancestral sequences always maintained a charge balance between mature defensin and propiece, and
changes in the net positive charge of the mature defensin were balanced by corresponding changes in the propiece. The results
support the hypothesis that, in the evolution of these proteins, amino acid changes have occurred in a coordinated fashion
so as to preserve an adaptive phenotype.
Received: 23 October 1996 / Accepted: 7 January 1997 相似文献
15.
Francesco Frati Chris Simon Jack Sullivan David L. Swofford 《Journal of molecular evolution》1997,44(2):145-158
The sequence of the mitochondrial COII gene has been widely used to estimate phylogenetic relationships at different taxomonic
levels across insects. We investigated the molecular evolution of the COII gene and its usefulness for reconstructing phylogenetic
relationships within and among four collembolan families. The collembolan COII gene showed the lowest A + T content of all
insects so far examined, confirming that the well-known A + T bias in insect mitochondrial genes tends to increase from the
basal to apical orders. Fifty-seven percent of all nucleotide positions were variable and most of the third codon positions
appeared free to vary. Values of genetic distance between congeneric species and between families were remarkably high; in
some cases the latter were higher than divergence values between other orders of insects. The remarkably high divergence levels
observed here provide evidence that collembolan taxa are quite old; divergence levels among collembolan families equaled or
exceeded divergences among pterygote insect orders. Once the saturated third-codon positions (which violated stationarity
of base frequencies) were removed, the COII sequences contained phylogenetic information, but the extent of that information
was overestimated by parsimony methods relative to likelihood methods. In the phylogenetic analysis, consistent statistical
support was obtained for the monophyly of all four genera examined, but relationships among genera/families were not well
supported. Within the genus Orchesella, relationships were well resolved and agreed with allozyme data. Within the genus Isotomurus, although three pairs of populations were consistently identified, these appeared to have arisen in a burst of evolution from
an earlier ancestor. Isotomurus italicus always appeared as basal and I. palustris appeared to harbor a cryptic species, corroborating allozyme data.
Received: 12 January 1996 / Accepted: 10 August 1996 相似文献
16.
Satoru Kanai Reiko Kikuno Hiroyuki Toh Haruko Ryo Takeshi Todo 《Journal of molecular evolution》1997,45(5):535-548
The photolyase–blue-light photoreceptor family is composed of cyclobutane pyrimidine dimer (CPD) photolyases, (6-4) photolyases,
and blue-light photoreceptors. CPD photolyase and (6-4) photolyase are involved in photoreactivation for CPD and (6-4) photoproducts,
respectively. CPD photolyase is classified into two subclasses, class I and II, based on amino acid sequence similarity. Blue-light
photoreceptors are essential light detectors for the early development of plants. The amino acid sequence of the receptor
is similar to those of the photolyases, although the receptor does not show the activity of photoreactivation. To investigate
the functional divergence of the family, the amino acid sequences of the proteins were aligned. The alignment suggested that
the recognition mechanisms of the cofactors and the substrate of class I CPD photolyases (class I photolyases) are different
from those of class II CPD photolyases (class II photolyases). We reconstructed the phylogenetic trees based on the alignment
by the NJ method and the ML method. The phylogenetic analysis suggested that the ancestral gene of the family had encoded
CPD photolyase and that the gene duplication of the ancestral proteins had occurred at least eight times before the divergence
between eubacteria and eukaryotes.
Received: 23 October 1996 / Accepted: 1 April 1997 相似文献
17.
The Old World sparrows (genus Passer) phylogeography and their relative abundance of nuclear mtDNA pseudogenes 总被引:2,自引:0,他引:2
Allende LM Rubio I Ruíz-Del-Valle V Guillén J Martínez-Laso J Lowy E Varela P Zamora J Arnaiz-Villena A 《Journal of molecular evolution》2001,53(2):144-154
The phylogenetic relationships of genus Passer (Old World sparrows) have been studied with species covering their complete world living range. Mitochondrial (mt) cyt b
genes and pseudogenes have been analyzed, the latter being strikingly abundant in genus Passer compared with other studied songbirds. The significance of these Passer pseudogenes is presently unclear. The mechanisms by which mt cyt b genes become pseudogenes after nuclear translocation are
discussed together with their mode of evolution, i.e., transition/transversion mitochondrial ratio is decreased in the nucleus,
as is the constraint for variability at the three codon positions. However, the skewed base composition according to codon
position (in 1st position the percentage is very similar for the four bases, in 2nd position there are fewer percentage of A and G and more percentage of T, and in 3rd codon position fewer percentage of G and T and is very rich in A and C) is maintained in the translocated nuclear pseudogenes.
Different nuclear internal mechanisms and/or selective pressures must exist for explaining this nuclear/mitochondrial differential
DNA base evolutive variability. Also, the phylogenetic usefulness of pseudogenes for defining relationships between closely
related lineages is stressed. The analyses suggest that the primitive genus Passer species comes from Africa, the Cape sparrow
being the oldest: P. hispaniolensis italiae is more likely conspecific to P. domesticus than to P. hispaniolensis. Also, Passer species are not included within weavers or Estrildinae or Emberizinae, as previously suggested. European and American Emberizinae sparrows are closely related to each other and seem to be the earliest species that radiated among the studied songbirds
(all in the Miocene Epoch).
Received: 29 November 2000 / Accepted: 22 March 2001 相似文献
18.
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
19.
Gene structure of a chlorophyll a/c-binding protein from a brown alga: Presence of an intron and phylogenetic implications 总被引:5,自引:0,他引:5
Lise Caron Dominique Douady Michelle Quinet-Szely Susan de Goër Claire Berkaloff 《Journal of molecular evolution》1996,43(3):270-280
A Laminaria saccharina genomic library in the phage EMBL 4 was used to isolate and sequence a full-length gene encoding a fucoxanthin-chlorophyll
a/c-binding protein. Contrary to diatom homologues, the coding sequence is interrupted by an intron of about 900 bp which
is located in the middle of the transit peptide. The deduced amino acid sequence of the mature protein is very similar to
those of related proteins from Macrocystis pyrifera (Laminariales) and, to a lesser extent, to those from diatoms and Chrysophyceae. Seven of the eight putative chlorophyll-binding
amino acids determined in green plants are also present. Alignments of different sequences related to the light-harvesting
proteins (LHC) demonstrate a structural similarity among the three transmembrane helices and suggest a unique ancestral helix
preceded by two β-turns. The β-turns are conserved in front of the second helices of the chlorophyll a/c proteins more so
than in chlorophyll a/b proteins. Phylogenetic trees generated from sequence data indicate that fucoxanthin-chlorophyll-binding
proteins diverged prior to the separation of photosystem I and photosystem II LHC genes of green plants. Among the fucoxanthin-containing
algae, LHC I or II families could not be distinguished at this time.
Received: 14 February 1996 / Accepted: 4 April 1996 相似文献
20.
J.D.H. Bursell J. Kirk S.T. Hall A.M. Gero K. Kirk 《The Journal of membrane biology》1996,154(2):131-141
The unicellular protozoan parasite, Crithidia luciliae, responded to osmotic swelling by undergoing a regulatory volume decrease. This process was accompanied by the efflux of amino
acids (predominantly alanine, proline and glycine). The relative loss of the electroneutral amino acids proline, valine, alanine
and glycine was greater than that for the anionic amino acid, glutamate; there was negligible loss of the cationic amino acids,
lysine, arginine and ornithine. The characteristics of amino acid release were investigated using a radiolabeled form of the
nonmetabolized alanine analogue α-aminoisobutyrate. α-Aminoisobutyrate efflux was activated within a few seconds of a reduction
of the osmolality, and inactivated rapidly (again within a few seconds) on restoration of isotonicity. The initial rate of
efflux of α-aminoisobutyrate from cells in hypotonic medium was unaffected by the extracellular amino acid concentration.
Hypotonically activated α-aminoisobutyrate efflux (as well as the associated regulatory volume decrease) was inhibited by
the sulfhydryl reagent N-ethylmaleimide but was not inhibited by a range of anion transport blockers. As in the efflux experiments, unidirectional
influx rates for α-aminoisobutyrate increased markedly following reduction of the osmolality, consistent with the swelling-activated
amino acid release mechanism allowing the flux of solutes in both directions. Hypotonically activated α-aminoisobutyrate influx
showed no tendency to saturate up to an extracellular concentration of 50 mm. The functional characteristics of the amino acid release mechanism are those of a channel, with a preference for electroneutral
and anionic amino acids over cationic amino acids. However, the pharmacology of the system differs from that of the anion-selective
channels that are thought to mediate the volume-regulatory efflux of organic osmolytes from vertebrate cells.
Received: 13 May 1996/Revised: 9 July 1996 相似文献