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1.
We present a novel hypothesis for the origin of the eukaryotic cell, or eukaryogenesis, based on a metabolic symbiosis (syntrophy)
between a methanogenic archaeon (methanobacterial-like) and a δ-proteobacterium (an ancestral sulfate-reducing myxobacterium).
This syntrophic symbiosis was originally mediated by interspecies H2 transfer in anaerobic, possibly moderately thermophilic, environments. During eukaryogenesis, progressive cellular and genomic
cointegration of both types of prokaryotic partners occurred. Initially, the establishment of permanent consortia, accompanied
by extensive membrane development and close cell–cell interactions, led to a highly evolved symbiotic structure already endowed
with some primitive eukaryotic features, such as a complex membrane system defining a protonuclear space (corresponding to
the archaeal cytoplasm), and a protoplasmic region (derived from fusion of the surrounding bacterial cells). Simultaneously,
bacterial-to-archaeal preferential gene transfer and eventual replacement took place. Bacterial genome extinction was thus
accomplished by gradual transfer to the archaeal host, where genes adapted to a new genetic environment. Emerging eukaryotes
would have inherited archaeal genome organization and dynamics and, consequently, most DNA-processing information systems.
Conversely, primordial genes for social and developmental behavior would have been provided by the ancient myxobacterial symbiont.
Metabolism would have been issued mainly from the versatile bacterial organotrophy, and progressively, methanogenesis was
lost.
Received: 5 January 1998 / Accepted: 18 March 1998 相似文献
2.
The Path from the RNA World 总被引:1,自引:0,他引:1
We describe a sequential (step by step) Darwinian model for the evolution of life from the late stages of the RNA world through
to the emergence of eukaryotes and prokaryotes. The starting point is our model, derived from current RNA activity, of the
RNA world just prior to the advent of genetically-encoded protein synthesis. By focusing on the function of the protoribosome
we develop a plausible model for the evolution of a protein-synthesizing ribosome from a high-fidelity RNA polymerase that
incorporated triplets of oligonucleotides. With the standard assumption that during the evolution of enzymatic activity, catalysis
is transferred from RNA → RNP → protein, the first proteins in the ``breakthrough organism' (the first to have encoded protein
synthesis) would be nonspecific chaperone-like proteins rather than catalytic. Moreover, because some RNA molecules that pre-date
protein synthesis under this model now occur as introns in some of the very earliest proteins, the model predicts these particular
introns are older than the exons surrounding them, the ``introns-first' theory. Many features of the model for the genome
organization in the final RNA world ribo-organism are more prevalent in the eukaryotic genome and we suggest that the prokaryotic
genome organization (a single, circular genome with one center of replication) was derived from a ``eukaryotic-like' genome
organization (a fragmented linear genome with multiple centers of replication). The steps from the proposed ribo-organism
RNA genome → eukaryotic-like DNA genome → prokaryotic-like DNA genome are all relatively straightforward, whereas the transition
prokaryotic-like genome → eukaryotic-like genome appears impossible under a Darwinian mechanism of evolution, given the assumption
of the transition RNA → RNP → protein. A likely molecular mechanism, ``plasmid transfer,' is available for the origin of
prokaryotic-type genomes from an eukaryotic-like architecture. Under this model prokaryotes are considered specialized and
derived with reduced dependence on ssRNA biochemistry. A functional explanation is that prokaryote ancestors underwent selection
for thermophily (high temperature) and/or for rapid reproduction (r selection) at least once in their history.
Received: 14 January 1997 / Accepted: 19 May 1997 相似文献
3.
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
4.
The AAA proteins (ATPases Associated with a variety of cellular Activities) are found in eubacterial, archaebacterial, and eukaryotic species and participate in a large number of cellular
processes, including protein degradation, vesicle fusion, cell cycle control, and cellular secretory processes. The AAA proteins
are characterized by the presence of a 230 to 250-amino acid ATPase domain referred to as the Conserved ATPase Domain or CAD. Phylogenetic analysis of 133 CAD sequences from 38 species reveal that AAA CADs are organized into discrete
groups that are related not only in structure but in cellular function. Evolutionary analyses also indicate that the CAD was
present in the last common ancestor of eubacteria, archaebacteria, and eukaryotes. The eubacterial CADs are found in metalloproteases,
while CAD-containing proteins in the archaebacterial and eukaryotic lineages appear to have diversified by a series of gene
duplication events that lead to the establishment of different functional AAA proteins, including proteasomal regulatory,
NSF/Sec, and Pas proteins. The phylogeny of the CADs provides the basis for establishing the patterns of evolutionary change
that characterize the AAA proteins.
Received: 28 January 1997 / Accepted: 8 May 1997 相似文献
5.
Masaharu Takemura 《Journal of molecular evolution》2001,52(5):419-425
A number of molecular forms of DNA polymerases have been reported to be involved in eukaryotic nuclear DNA replication, with
contributions from α-, δ-, and ε-polymerases. It has been reported that δ-polymerase possessed a central role in DNA replication
in archaea, whose ancestry are thought to be closely related to the ancestor of eukaryotes. Indeed, in vitro experiment shown
here suggests that δ-polymerase has the potential ability to start DNA synthesis immediately after RNA primer synthesis. Therefore,
the question arises, where did the α-polymerase come from? Phylogenetic analysis based on the nucleotide sequence of several
conserved regions reveals that two poxviruses, vaccinia and variola viruses, have polymerases similar to eukaryotic α-polymerase
rather than δ-polymerase, while adenovirus, herpes family viruses, and archaeotes have eukaryotic δ-like polymerases, suggesting
that the eukaryotic α-polymerase gene is derived from a poxvirus-like organism, which had some eukaryote-like characteristics.
Furthermore, the poxvirus's proliferation independent from the host-cell nucleus suggests the possibility that this virus
could infect non-nucleated cells, such as ancestral eukaryotes. I wish to propose here a new hypothesis for the origin of
the eukaryotic nucleus, posing symbiotic contact of an orthopoxvirus ancestor with an archaebacterium, whose genome already
had a δ-like polymerase gene.
Received: 26 October 2000 / Accepted: 16 January 2001 相似文献
6.
Trevor Lithgow André Schneider 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2010,365(1541):799-817
All eukaryotes require mitochondria for survival and growth. The origin of mitochondria can be traced down to a single endosymbiotic event between two probably prokaryotic organisms. Subsequent evolution has left mitochondria a collection of heterogeneous organelle variants. Most of these variants have retained their own genome and translation system. In hydrogenosomes and mitosomes, however, the entire genome was lost. All types of mitochondria import most of their proteome from the cytosol, irrespective of whether they have a genome or not. Moreover, in most eukaryotes, a variable number of tRNAs that are required for mitochondrial translation are also imported. Thus, import of macromolecules, both proteins and tRNA, is essential for mitochondrial biogenesis. Here, we review what is known about the evolutionary history of the two processes using a recently revised eukaryotic phylogeny as a framework. We discuss how the processes of protein import and tRNA import relate to each other in an evolutionary context. 相似文献
7.
Heat Shock Protein 70 Family: Multiple Sequence Comparisons, Function, and Evolution 总被引:14,自引:0,他引:14
The heat shock protein 70 kDa sequences (HSP70) are of great importance as molecular chaperones in protein folding and transport.
They are abundant under conditions of cellular stress. They are highly conserved in all domains of life: Archaea, eubacteria,
eukaryotes, and organelles (mitochondria, chloroplasts). A multiple alignment of a large collection of these sequences was
obtained employing our symmetric-iterative ITERALIGN program (Brocchieri and Karlin 1998). Assessments of conservation are
interpreted in evolutionary terms and with respect to functional implications. Many archaeal sequences (methanogens and halophiles)
tend to align best with the Gram-positive sequences. These two groups also miss a signature segment [about 25 amino acids
(aa) long] present in all other HSP70 species (Gupta and Golding 1993). We observed a second signature sequence of about 4
aa absent from all eukaryotic homologues, significantly aligned in all prokaryotic sequences. Consensus sequences were developed
for eight groups [Archaea, Gram-positive, proteobacterial Gram-negative, singular bacteria, mitochondria, plastids, eukaryotic
endoplasmic reticulum (ER) isoforms, eukaryotic cytoplasmic isoforms]. All group consensus comparisons tend to summarize better
the alignments than do the individual sequence comparisons. The global individual consensus ``matches' 87% with the consensus
of consensuses sequence. A functional analysis of the global consensus identifies a (new) highly significant mixed charge
cluster proximal to the carboxyl terminus of the sequence highlighting the hypercharge run EEDKKRRER (one-letter aa code used).
The individual Archaea and Gram-positive sequences contain a corresponding significant mixed charge cluster in the location
of the charge cluster of the consensus sequence. In contrast, the four Gram-negative proteobacterial sequences of the alignment
do not have a charge cluster (even at the 5% significance level). All eukaryotic HSP70 sequences have the analogous charge
cluster. Strikingly, several of the eukaryotic isoforms show multiple mixed charged clusters. These clusters were interpreted
with supporting data related to HSP70 activity in facilitating chaperone, transport, and secretion function. We observed that
the consensus contains only a single tryptophan residue and a single conserved cysteine. This is interpreted with respect
to the target rule for disaggregating misfolded proteins. The mitochondrial HSP70 connections to bacterial HSP70 are analyzed,
suggesting a polyphyletic split of Trypanosoma and Leishmania protist mitochondrial (Mt) homologues separated from Mt-animal/fungal/plant homologues. Moreover, the HSP70 sequences from
the amitochondrial Entamoeba histolytica and Trichomonas vaginalis species were analyzed. The E. histolytica HSP70 is most similar to the higher eukaryotic cytoplasmic sequences, with significantly weaker alignments to ER sequences
and much diminished matching to all eubacterial, mitochondrial, and chloroplast sequences. This appears to be at variance
with the hypothesis that E. histolytica rather recently lost its mitochondrial organelle. T. vaginalis contains two HSP70 sequences, one Mt-like and the second similar to eukaryotic cytoplasmic sequences suggesting two diverse
origins.
Received: 29 January 1998 / Accepted: 14 May 1998 相似文献
8.
Saier MH 《The Journal of membrane biology》2000,175(3):165-180
Channel-forming proteins/peptides fall into over 100 currently recognized families, most of which are restricted to prokaryotes
or eukaryotes, but a few of which are ubiquitous. These proteins fall into three major currently recognized classes: (i) α-helix-type
channels present in bacterial, archaeal and eukaryotic cytoplasmic and organellar membranes, (ii) β-barrel-type porins present
in the outer membranes of Gram-negative bacterial cells, mitochondria and chloroplasts, and (iii) protein/peptide toxins targeted
to the cytoplasmic membranes of cells other than those that synthesize the toxins. High-resolution 3-dimensional structural
data are available for representative proteins/peptides of all three of these channel-forming types. Each type exhibits distinctive
features that distinguish them from the other channel protein types and from carriers. Structural, functional, and evolutionary
aspects of transmembrane channel-formers are discussed.
Received: 10 September 1999/Revised: 11 February 2000 相似文献
9.
Jürgen Wastl Martin Fraunholz Stefan Zauner Susan Douglas Uwe-G. Maier 《Journal of molecular evolution》1999,48(1):112-117
Cryptomonads, small biflagellate algae, contain four different genomes. In addition to the nucleus, mitochondrion, and chloroplast
is a fourth DNA-containing organelle the nucleomorph. Nucleomorphs result from the successive reduction of the nucleus of
an engulfed phototrophic eukaryotic endosymbiont by a secondary eukaryotic host cell. By sequencing the chloroplast genome
and the nucleomorph chromosomes, we identified a groEL homologue in the genome of the chloroplast and a related cpn60 in one of the nucleomorph chromosomes. The nucleomorph-encoded Cpn60 and the chloroplast-encoded GroEL correspond in each
case to one of the two divergent GroEL homologues in the cyanobacterium Synechocystis sp. PCC6803. The coexistence of divergent groEL/cpn60 genes in different genomes in one cell offers insights into gene transfer from evolving chloroplasts to cell nuclei and
convergent gene evolution in chlorophyll a/b versus chlorophyll a/c/phycobilin eukaryotic lineages.
Received: 24 April 1998 / Accepted: 12 June 1998 相似文献
10.
Computer analyses of various genome sequences revealed the existence of certain periodical patterns of adenine–adenine dinucleotides
(ApA). For each genome sequence of 13 eubacteria, 3 archaebacteria, 10 eukaryotes, 60 mitochondria, and 9 chloroplasts, we
counted frequencies of ApA dinucleotides at each downstream position within 50 bp from every ApA. We found that the complete
genomes of all three archaebacteria have clear ApA periodicities of about 10 bps. On the other hand, all of the 13 eubacteria
we analyzed were found to have an ApA periodicity of about 11 bp. Similar periodicities exist in the 10 eukaryotes, although
higher organisms such as primates tend to have weaker periodic patterns. None of the mitochondria and chroloplasts we analyzed
showed an evident periodic pattern.
Received: 3 November 1998 / Accepted: 24 March 1999 相似文献
11.
Patrick J. Keeling Naomi M. Fast Geoff I. McFadden 《Journal of molecular evolution》1998,47(6):649-655
Eubacterial and eukaryotic translation initiation systems have very little in common, and therefore the evolutionary events
that gave rise to these two disparate systems are difficult to ascertain. One common feature is the presence of initiation,
elongation, and release factors belonging to a large GTPase superfamily. One of these initiation factors, the γ subunit of
initiation factor 2 (eIF-2γ), is found only in eukaryotes and archaebacteria. We have sequenced eIF-2γ gene fragments from
representative diplomonads, parabasalia, and microsporidia and used these new sequences together with new archaebacterial
homologues to examine the phylogenetic position of eIF-2γ within the GTPase superfamily. The archaebacterial and eukaryotic
eIF-2γ proteins are found to be very closely related, and are in turn related to SELB, the selenocysteine-specific elongation
factor from eubacteria. The overall topology of the GTPase tree further suggests that the eIF-2γ/SELB group may represent
an ancient subfamily of GTPases that diverged prior to the last common ancestor of extant life.
Received: 2 January 1998 / Accepted: 1 June 1998 相似文献
12.
The Rooting of the Universal Tree of Life Is Not Reliable 总被引:19,自引:0,他引:19
Several composite universal trees connected by an ancestral gene duplication have been used to root the universal tree of
life. In all cases, this root turned out to be in the eubacterial branch. However, the validity of results obtained from comparative
sequence analysis has recently been questioned, in particular, in the case of ancient phylogenies. For example, it has been
shown that several eukaryotic groups are misplaced in ribosomal RNA or elongation factor trees because of unequal rates of
evolution and mutational saturation. Furthermore, the addition of new sequences to data sets has often turned apparently reasonable
phylogenies into confused ones. We have thus revisited all composite protein trees that have been used to root the universal
tree of life up to now (elongation factors, ATPases, tRNA synthetases, carbamoyl phosphate synthetases, signal recognition
particle proteins) with updated data sets. In general, the two prokaryotic domains were not monophyletic with several aberrant
groupings at different levels of the tree. Furthermore, the respective phylogenies contradicted each others, so that various
ad hoc scenarios (paralogy or lateral gene transfer) must be proposed in order to obtain the traditional Archaebacteria–Eukaryota
sisterhood. More importantly, all of the markers are heavily saturated with respect to amino acid substitutions. As phylogenies
inferred from saturated data sets are extremely sensitive to differences in evolutionary rates, present phylogenies used to
root the universal tree of life could be biased by the phenomenon of long branch attraction. Since the eubacterial branch
was always the longest one, the eubacterial rooting could be explained by an attraction between this branch and the long branch
of the outgroup. Finally, we suggested that an eukaryotic rooting could be a more fruitful working hypothesis, as it provides,
for example, a simple explanation to the high genetic similarity of Archaebacteria and Eubacteria inferred from complete genome
analysis. 相似文献
13.
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
14.
Molecular and morphological evidence points to the ancyromonad Ancyromonas as a plausible candidate for the closest relative to the common ancestor of metazoans, fungi, and choanoflagellates (the
Opisthokonta). Using 18S rDNA sequences from most of the major eukaryotic lineages, maximum-likelihood, minimum-evolution,
and maximum-parsimony analyses yielded congruent phylogenies supporting this hypothesis. Combined with ultrastructural similarities
between Ancyromonas and opisthokonts, the evidence presented here suggests that Ancyromonas may form an independent lineage, the Ancyromonadida Cavalier-Smith 1997, closer in its relationship to the opisthokonts than
is its nearest protist relatives, the Apusomonadida. However, the very low bootstrap support for deep nodes and hypothesis
testing indicate that the resolving power of 18S rDNA sequences is limited for examining this aspect of eukaryotic phylogeny.
Alternate branching positions for the Ancyromonas lineage cannot be robustly rejected, revealing the importance of ultrastructure when examining the origins of multicellularity.
The future use of a multigene approach may additionally be needed to resolve this aspect of eukaryotic phylogeny.
Received: 27 March 2000 / Accepted: 12 June 2000 相似文献
15.
Miklós Müller Marek Mentel Jaap J. van Hellemond Katrin Henze Christian Woehle Sven B. Gould Re-Young Yu Mark van der Giezen Aloysius G. M. Tielens William F. Martin 《Microbiology and molecular biology reviews》2012,76(2):444-495
Summary: Major insights into the phylogenetic distribution, biochemistry, and evolutionary significance of organelles involved in ATP synthesis (energy metabolism) in eukaryotes that thrive in anaerobic environments for all or part of their life cycles have accrued in recent years. All known eukaryotic groups possess an organelle of mitochondrial origin, mapping the origin of mitochondria to the eukaryotic common ancestor, and genome sequence data are rapidly accumulating for eukaryotes that possess anaerobic mitochondria, hydrogenosomes, or mitosomes. Here we review the available biochemical data on the enzymes and pathways that eukaryotes use in anaerobic energy metabolism and summarize the metabolic end products that they generate in their anaerobic habitats, focusing on the biochemical roles that their mitochondria play in anaerobic ATP synthesis. We present metabolic maps of compartmentalized energy metabolism for 16 well-studied species. There are currently no enzymes of core anaerobic energy metabolism that are specific to any of the six eukaryotic supergroup lineages; genes present in one supergroup are also found in at least one other supergroup. The gene distribution across lineages thus reflects the presence of anaerobic energy metabolism in the eukaryote common ancestor and differential loss during the specialization of some lineages to oxic niches, just as oxphos capabilities have been differentially lost in specialization to anoxic niches and the parasitic life-style. Some facultative anaerobes have retained both aerobic and anaerobic pathways. Diversified eukaryotic lineages have retained the same enzymes of anaerobic ATP synthesis, in line with geochemical data indicating low environmental oxygen levels while eukaryotes arose and diversified. 相似文献
16.
Acquisition of mitochondria by the ancestor of all living eukaryotes represented a crucial milestone in the evolution of the eukaryotic cell. Nevertheless, a number of anaerobic unicellular eukaryotes have secondarily discarded certain mitochondrial features, leading to modified organelles such as hydrogenosomes and mitosomes via degenerative evolution. These mitochondrion-derived organelles have lost many of the typical characteristics of aerobic mitochondria, including certain metabolic pathways, morphological traits, and, in most cases, the organellar genome. So far, the evolutionary pathway leading from aerobic mitochondria to anaerobic degenerate organelles has remained unclear due to the lack of examples representing intermediate stages. The human parasitic stramenopile Blastocystis is a rare example of an anaerobic eukaryote with organelles that have retained some mitochondrial characteristics, including a genome, whereas they lack others, such as cytochromes. Here we report the sequence and comparative analysis of the organellar genome from two different Blastocystis isolates as well as a comparison to other genomes from stramenopile mitochondria. Analysis of the characteristics displayed by the unique Blastocystis organelle genome gives us an insight into the initial evolutionary steps that may have led from mitochondria to hydrogenosomes and mitosomes. 相似文献
17.
Eukaryotes have long been thought to have arisen by evolving a nucleus, endomembrane, and cytoskeleton. In contrast, it was recently proposed that the first complex cells, which were actually proto-eukaryotes, arose simultaneously with the acquisition of mitochondria. This so-called symbiotic association hypothesis states that eukaryotes emerged when some ancient anaerobic archaebacteria (hosts) engulfed respiring alpha-proteobacteria (symbionts), which evolved into the first energy-producing organelles. Therefore, the intracellular compartmentalization of the energy-converting metabolism that was bound originally to the plasma membrane appears to be the key innovation towards eukaryotic genome and cellular organization. The novel energy metabolism made it possible for the nucleotide synthetic apparatus of cells to be no longer limited by subsaturation with substrates and catalytic components. As a consequence, a considerable increase has occurred in the size and complexity of eukaryotic genomes, providing the genetic basis for most of the further evolutionary changes in cellular complexity. On the other hand, the active uptake of exogenous DNA, which is general in bacteria, was no longer essential in the genome organization of eukaryotes. The mitochondrion-driven scenario for the first eukaryotes explains the chimera-like composition of eukaryotic genomes as well as the metabolic and cellular organization of eukaryotes. 相似文献
18.
Galitskiĭ VA 《Tsitologiia》2005,47(2):103-120
The unified conception of the origin of eukaryotic cells has been proposed. In the author's opinion, evolutionary transformation of prokaryotic cell into eukaryotic cell took place 3.3-1.4 billion years ago and involved the next four stages: 1) the appearance of intracellular membranes due to prokaryotic cell plasmalemma invaginating into its cytoplasm; 2) the cell nucleus formation by the double sheet of intracellular membrane surrounding and sequestrating genetic material of the cell; 3) the appearance of cytoskeleton in parallel with mitotic spindle formation and gradual transition from prokaryotic way of cell division to mitosis; 4) the establishment of symbiosis between the evolving nucleated cell and prokaryotic microorganicsms that subsequently transform into mitochondria and chloroplasts. Apoptosis of cells of the present day multicellular eukaryotic organisms is supposed to be an evolutionary altered response of mitochondrian predecessors to the influence of factors, which are able to damage eukaryotic host cell. The initial biological significance of this reaction pertained to attempts of endosymbionts to leave the host cell as soon as possible, if the probability of its irreversible injury was very high, and by this to escape from their death. It is possible that numerous proteins, known as sensors or transducers of proapoptotic signals in Bcl-2--p53-dependent apoptotic pathway, were initially encoded by mitochondrial genome, whereas antiapoptotic factors and also components of receptor-mediated and granzyme B perforin dependent apoptotic pathways have cellular origin. 相似文献
19.
A Novel Family of Ubiquitous Heavy Metal Ion Transport Proteins 总被引:33,自引:0,他引:33
We describe a novel diverse family of metal ion transporter (CDF) proteins (the cation diffusion facilitator (CDF) family)
with members occurring in both prokaryotes and eukaryotes. Thirteen sequenced protein members of the CDF family have been
identified, several of which have been shown to transport cobalt, cadmium and/or zinc. All members of the CDF family possess
six putative transmembrane spanners with strongest conservation in the four N-terminal spanners, and on the basis of the analyses,
we present a unified structural model. Members of the family are shown to exhibit an unusual degree of size variation, sequence
divergence, and differences in cell localization and polarity. The phylogenetic tree for the CDF family reveals that prokaryotic
and eukaryotic proteins cluster separately. It allows functional predictions for some uncharacterized members of this family.
A signature sequence specific for the CDF family is derived.
Received: 15 July 1996/Revised: 21 October 1996 相似文献
20.
The evolutionary processes underlying the differentness of prokaryotic and eukaryotic cells and the origin of the latter's organelles are still poorly understood. For about 100 years, the principle of endosymbiosis has figured into thoughts as to how these processes might have occurred. A number of models that have been discussed in the literature and that are designed to explain this difference are summarized. The evolutionary histories of the enzymes of anaerobic energy metabolism (oxygen-independent ATP synthesis) in the three basic types of heterotrophic eukaryotes those that lack organelles of ATP synthesis, those that possess mitochondria and those that possess hydrogenosomes--play an important role in this issue. Traditional endosymbiotic models generally do not address the origin of the heterotrophic lifestyle and anaerobic energy metabolism in eukaryotes. Rather they take it as a given, a direct inheritance from the host that acquired mitochondria. Traditional models are contrasted to an alternative endosymbiotic model (the hydrogen hypothesis), which addresses the origin of heterotrophy and the origin of compartmentalized energy metabolism in eukaryotes. 相似文献