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At least 631 records · Page 35Linked to original sources
PubMed2000

Mitochondrial proteins at unexpected cellular locations: export of proteins from mitochondria from an evolutionary perspective.

Researchers in a wide variety of unrelated areas studying functions of different proteins are unexpectedly finding that their proteins of interest are actually mitochondrial proteins, although functions would appear to be extramitochondrial. We review the leading current examples of mitochondrial macromolecules indicated to be also present outside of mitochondria that apparently exit from mitochondria to arrive at their destinations. Mitochondrial chaperones, which have been implicated in growth and development, autoimmune diseases, cell mortality, antigen presentation, apoptosis, and resistance to antimitotic drugs, provide some of the best studied examples pointing to roles for mitochondria and mitochondrial proteins in diverse cellular phenomena. To explain the observations, we propose that specific export mechanisms exist by which certain proteins exit mitochondria, allowing these proteins to have additional functions at specific extramitochondrial sites. Several possible mechanisms by which mitochondrial proteins could be exported are discussed. Gram-negative proteobacteria, from which mitochondria evolved, contain a number of different mechanisms for protein export. It is likely that mitochondria either retained or evolved export mechanisms for certain specific proteins.

Animals↗
PubMed1997

Identification of a gene in the euryarchaeal Thermococcus species AN1 encoding a protein homologous to the alpha subunit of the eukaryal signal recognition particle (SRP) receptor.

We describe here the sequence and transcriptional analysis of a gene from the euryarchaeal Thermococcus species AN1 (DSM 2770) encoding a protein homologous to the alpha subunit of the eukaryal SRP receptor (SR alpha). The AN1 protein is found to share the highest degree of homology with the only other described archaeal SR alpha homolog characterized from the hyperthermophilic crenarchaeal Sulfolobus solfataricus. Sequence analysis of the translation of the AN1 gene reveals the presence of the following previously described domains: an N-terminal alpha domain rich in acidic and basic residues; an X domain and four GTP binding motifs (G1-G4). A putative guanine nucleotide dissociation stimulator binding element is also present. The AN1 SR alpha protein would now represent the shortest variant of this expanding family with 329 residues and a predicted molecular weight of 36.4 kDa. A Northern analysis indicates that the AN1 SR alpha protein gene transcript is present at low levels suggesting that SR alpha is likely to be only a minor cell constituent. The presence of an SR alpha homolog in another kingdom within the archaeal domain possessing the full suite of conserved motifs is significant in several respects. It not only supports the monophyletic character of the domain Archaea but suggests that these homologs have similar functions in these organisms and emphasises the ancient origins of the protein export machinery.

Amino Acid Sequence↗
PubMed2002

A PUF family portrait: 3'UTR regulation as a way of life.

In eukaryotic cells, mRNAs are exquisitely controlled, often through regulatory elements in their 3' untranslated regions (3'UTRs). Proteins that bind to those sites are key players in controlling mRNA stability, translation and localization. One family of regulatory proteins--the PUF proteins--are not only structurally related, but also bind to 3'UTRs and modulate mRNA expression in a wide variety of eukaryotic species. They do so either by enhancing turnover or repressing translation, and act combinatorially with other regulatory proteins. Here, we discuss the evolution, biological function and mechanisms of action of the PUF protein family, and suggest that a primordial function of PUF proteins is to sustain mitotic proliferation of stem cells.

3' Untranslated Regions↗
PubMed1999

Nonequilibrium / nonlinear chemical oscillation in the virtual absence of gravity.

The Belousov-Zhabotinsky (BZ) reactions were used as typical examples of a nonlinear system far from equilibrium in connection with biological evolution. The virtual absence of gravity in the present work was given from the free-fall facility of Japan Microgravity Center (JAMIC) in Hokkaido. The reaction solution of BZ reaction was composed of bromate in sulfuric acid, 1,4-cyclohexanedione and ferroin to visualize the time development of patterns of chemical oscillations in the reaction-diffusion system. It is a bubble-free constitution in the aging of the reaction. Therefore, the setup constructed to collect image data via CCD cameras was simplified. The operation sequences of necessary devices were comprised of simple solid state relays which were started by a command from the operation room of JAMIC. The propagation profile of chemical patterns under microgravity of 10(-5) g was collected as image data for 9.8 s, and processed by a software of STM-STS2. In the aqueous solutions, propagation velocity of chemical patterns under microgravity was decreased to 80.9 % of that under normal gravity, owing to suppression of convection. On the other hand, in gel matrix, gravity did not influence the propagation velocity.

Bromates↗
PubMed1997

A quantum-theoretical approach to the phenomenon of directed mutations in bacteria (hypothesis).

The Darwinian paradigm of biological evolution is based on the independence of genetic variations from selection which occurs afterwards. However, according to the phenomenon of directed mutations, some genetic variations occur mostly when the conditions favorable for their growth are created. I propose that the explanation of this phenomenon should not rely on any special 'mechanism' for the appearance of directed mutations, but rather should be based on the principles of quantum theory. I consider a physical model of adaptation whereby a polarized photon, passing through a polarizer, changes its polarization according to the angle of the polarizer. This adaptation occurs by selection of the 'fitted' polarized state which exists as a component of superposition in the initial state of the photon. However, since the same state of the incoming photon should be decomposed differently depending on the angle of the polarizer, in this case the set of variations subjected to selection depends upon the selective conditions themselves. This reveals the crucial difference between this model of adaptation and canonical Darwinian selection. Based on this analogy, the capacity of a cell to grow in particular conditions is considered an observable of the cell; the plating experiments are interpreted as measurement of this observable. The only nontrivial suggestion of the paper states that the cell, analogously to the polarized photon, may be in a state of superposition of eigenfunctions of the operator which represents this observable, and with some probability can appear as a mutant upon the measurement. Alternative growth conditions correspond to the decomposition of the same state vector into a different superposition, consistent with measurement of a different observable and appearance of different mutants. Thus, consistent with the suggested analogy, directed mutations are explained as a result of random choice from the set of outcomes determined by the environment.

Adaptation, Physiological↗
PubMedDate not supplied

A new family of high-affinity ABC manganese and zinc permeases.

Phylogenetic analysis of 47 extracellular putative metal binding receptors (MBRs) belonging to the newly defined cluster suggests the existence of two subclusters. The question of substrate specificity of the corresponding ATP binding cassette (ABC) permeases is discussed, based on data collected from 19 of them concerning their regulation, metal requirement of permease mutants, metal uptake and metal binding. The proposal that the two subclusters correspond to paralogous metal permeases dedicated primarily to manganese and to zinc transport is made. The question of a direct role of MBRs as adhesins of Gram-positive bacteria is then discussed and the importance of metal permeases for cellular processes and host-bacteria interactions is reviewed.

ATP-Binding Cassette Transporters↗
PubMed1997

From nucleoporins to nuclear pore complexes.

One of the largest supramolecular assemblies in the eukaryotic cell, the nuclear pore complex, is now being dissected into its numerous molecular constituents. The combined use of biochemistry and genetics in yeast has made this rapid development possible. Although less is known about vertebrate nucleoporins, the first clues are now emerging about their in vivo function also. Much remains to be learned about nuclear pore complex assembly and function, however.

Amino Acid Sequence↗
PubMed2002

Down but not out.

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Biological Evolution↗