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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several lines of evidence indicate that a component of axonemes from Chlamydomonas flagella is similar to actin from rabbit skeletal muscle. The polypeptide has an apparent molecular weight of 42,000 and in a pH gradient has the electrophoretic behavior of beta-actin. It was co-polymerized with rabbit actin and purified by affinity chromatography on DNase I-Sepharose. Incomplete proteolysis of mixed 35S-labeled axonemal protein and cold rabbit actin formed similar sets of peptides as analyzed by one-dimensional gel electrophoresis. The actin-like protein and the tubulin appear to be present in the axoneme in the molar ratio 1:60.
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PMID:An actin-like protein is a component of axonemes from Chlamydomonas flagella. 42 78

Through the isolation of suppressors of temperature-sensitive flagellar assembly mutations at the FLA10 locus of Chlamydomonas reinhardtii, we have identified six other genes involved in flagellar assembly. Mutations at these suppressor loci, termed SUF1-SUF6, display allele specificity with respect to which fla10- mutant alleles they suppress. An additional mutation, apm1-122, which confers resistance to the plant herbicides amiprophos-methyl and oryzalin, was also found to interact with mutations at the FLA10 locus. The apm1-122 mutation in combination with three fla10- mutant alleles results in synthetic cold-sensitive cell division defects, and in combination with an additional pseudo-wild-type fla10- allele yields a synthetic temperature-sensitive flagellar motility phenotype. Based upon the genetic interactions of these loci, we propose that the FLA10 gene product interacts with multiple components of the flagellar apparatus and plays a role both in flagellar assembly and in the cell cycle.
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PMID:Genetic interactions at the FLA10 locus: suppressors and synthetic phenotypes that affect the cell cycle and flagellar function in Chlamydomonas reinhardtii. 187 15

Our investigations of the mating reaction of Chlamydomonas revealed a surprisingly intricate series of interrelated events. Adhering sites are moved to the flagellar tips in a fashion highly reminiscent of the capping of surface ligands over the centriolar regions of lymphocytes (28). Tipping is prevented by the gam-1 mutation and by agents that interact with tubulin; the molecular mechanism(s) for the inhibition effects are currently being sought. Tip locking appears to be accompanied by the accumulation of a dense material beneath the tip membrane, a postulated alteration of axonemal structure, and an immobilization of component(s) involved in surface motility. Two mating signals are then transduced to the locked-in cells who respond by shedding cell walls, activating mating structures, and fusing together. Signal transmission and/or reception is sensitive to such agents as trypsin, chymotrypsin, and cold temperature. Once zygotic cell fusion has occurred, tip unlocking and a reversal of the tip activation response appear to occur in parallel. Since all of these events can occur within 30 sec, the mating reaction serves as an experimental paradigm for studying rapid cellular responses to specific membrane-membrane interactions.
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PMID:Membrane-membrane and membrane-ligand interactions in Chlamydomonas mating. 738 32

Adaptive compensation of enzymatic activities is common among cold-living poikilotherms. Their enzymes often demonstrate higher activities at low temperatures than do homologs from temperate or thermophilic species. To understand the molecular features necessary for cold adaptation of microtubule motor proteins, we have initiated studies of the flagellar dynein ATPases of Antarctic fishes (body temperature range = -1.8 to +2 degrees C). Dyneins were isolated by high-salt extraction of demembranated sperm axonemes from the Antarctic yellowbelly rockcod, Notothenia coriiceps. Although solubilization of inner arms was incomplete, an inner arm dynein was recognized as a discrete complex containing one major dynein heavy chain (DHC) and sedimenting through sucrose gradients at approximately 12 S. Like inner arm dyneins from Chlamydomonas, the fish complex contained an actin-immunoreactive protein of 43 kDa and a 30-kDa protein. One isoform of the inner arm DHC gene family of N. coriiceps was detected by the polymerase chain reaction, and Southern analysis established that this DHC gene is present at one copy per haploid genome. Outer arm dynein was extracted quantitatively by high-salt treatment, contained two DHCs (one major, one minor), and sedimented through sucrose gradients as a polydisperse, aggregating system. Associated with the outer arm DHCs were five presumptive intermediate chains (ICs) of 66-91 kDa, immunologically defined by their cross-reactivity to four monoclonal antibodies specific for ICs from other organisms. The basal (non-microtubule-stimulated) specific ATPase activities of the N. coriiceps inner and outer arm dyneins were approximately 0.07 and approximately 0.04 micromol of P(i) min(-1) mg(-1), respectively, at 0 degrees C, attained their maxima (approximately 0.1 micromol of P(i) min(-1) mg(-1)) at 9 and 19 degrees C, respectively, and at higher temperatures declined substantially. Furthermore, the activities of the fish dyneins at temperatures < or = 15 degrees C were significantly larger than that of outer arm dynein from the mesophile Tetrahymena. These results suggest that the greater catalytic efficiencies of N. coriiceps inner and outer arm dyneins at low temperatures are due to enhanced polypeptide flexibility in the active sites of their protein subunits. We conclude that temperature adaptation of flagellar dyneins from Antarctic fishes is compatible with substantial conservation of primary and quaternary structure.
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PMID:Inner and outer arm axonemal dyneins from the Antarctic rockcod Notothenia coriiceps. 906 78

The alpha-tubulin genes from two psychrophilic algae belonging to the genus Chloromonas (here named ANT1 and ANT3) have been isolated and sequenced. The genes ant1 and ant3 contain 4 and 2 introns, respectively. The coding DNA sequences are 90% identical but the degree of isology is very high at the polypeptide level (more than 97% strict identities). The ANT1 and ANT3 alpha-tubulin amino acid sequences were compared to the corresponding sequence of the mesophilic alga Chlamydomonas reinhardtii. Of the 15 substitutions detected in ANT1 and/or ANT3, 5 are common to both psychrophilic algae. The recorded substitutions have been analyzed in terms of cold adaptation on the basis of the available three-dimensional structure of the alpha,beta-tubulin heterodimer from pig brain. Most of these are subtle changes, but two substitutions, M268V and A295V occurring in the region of interdimer contacts, could be of great significance for the cold stability of Antarctic algae microtubules due to the fact that the entropic control of microtubule assembly is particularly high in cold adaptes species.
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PMID:Protein adaptation to low temperatures: a comparative study of alpha-tubulin sequences in mesophilic and psychrophilic algae. 1048 78

The thermodynamic stability and temperature induced structural changes of oxidized thioredoxin h from Chlamydomonas reinhardtii have been studied using differential scanning calorimetry (DSC), near- and far-UV circular dichroism (CD), and fluorescence spectroscopies. At neutral pH, the heat induced unfolding of thioredoxin h is irreversible. The irreversibly unfolded protein is unable to refold due to the formation of soluble high-order oligomers. In contrast, at acidic pH the heat induced unfolding of thioredoxin h is fully reversible and thus allows the thermodynamic stability of this protein to be characterized. Analysis of the heat induced unfolding at acidic pH using calorimetric and spectroscopic methods shows that the heat induced denaturation of thioredoxin h can be well approximated by a two-state transition. The unfolding of thioredoxin h is accompanied by a large heat capacity change [6.0 +/- 1.0 kJ/(mol.K)], suggesting that at low pH a cold denaturation should be observed at the above-freezing temperatures for this protein. All used methods (DSC, near-UV CD, far-UV CD, Trp fluorescence) do indeed show that thioredoxin h undergoes cold denaturation at pH <2.5. The cold denaturation of thioredoxin h cannot, however, be fitted to a two-state model of unfolding. Furthermore, according to the far-UV CD, thioredoxin h is fully unfolded at pH 2.0 and 0 degrees C, whereas the other three methods (near-UV CD, fluorescence, and DSC) indicate that under these conditions 20-30% of the protein molecules are still in the native state. Several alternative mechanisms explaining these results such as structural differences in the heat and cold denatured state ensembles and the two-domain structure of thioredoxin h are discussed.
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PMID:Difference in the mechanisms of the cold and heat induced unfolding of thioredoxin h from Chlamydomonas reinhardtii: spectroscopic and calorimetric studies. 1099 55

The alga Chlamydomonas nivalis lives in a high-light, cold environment: persistent alpine snowfields. Since the algae in snow receive light from all angles, the photon fluence rate is the critical parameter for photosynthesis, but it is rarely measured. We measured photon irradiance and photon fluence rate in the snow that contained blooms of C. nivalis. On a cloudless day the photon fluence rate at the snow surface was nearly twice the photon irradiance, and it can be many times greater than the photon irradiance when the solar angle is low or the light is diffuse. Beneath the surface the photon fluence rate can be five times the photon irradiance. Photon irradiance and photon fluence rate declined exponentially with depth, approximating the Bouguer-Lambert relationship. We used an integrating sphere to measure the spectral characteristics of a monolayer of cells and microscopic techniques to examine the spectral characteristics of individual cells. Astaxanthin blocked blue light and unknown absorbers blocked UV radiation; the penetration of these wavelengths through whole cells was negligible. We extracted astaxanthin, measured absorbance on a per-cell basis and estimated that the layer of astaxanthin within cells would allow only a small percentage of the blue light to reach the chloroplast, potentially protecting the chloroplast from excessive light.
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PMID:The light environment and cellular optics of the snow alga Chlamydomonas nivalis (Bauer) Wille. 1142 Oct 66

Aplanospores of Chlamydomonas nivalis are frequently found in high-altitude, persistent snowfields where they are photosynthetically active despite cold temperatures and high levels of visible and ultraviolet (UV) radiation. The goals of this work were to characterize the UV environment of the cells in the snow and to investigate the existence and localization of screening compounds that might prevent UV damage. UV irradiance decreased precipitously in snow, with UV radiation of wavelengths 280-315 nm and UV radiation of wavelengths 315-400 nm dropping to 50% of incident levels in the top 1 and 2 cm, respectively. Isolated cell walls exhibited UV absorbance, possibly by sporopollenin, but this absorbance was weak in images of broken or plasmolyzed cells observed through a UV microscope. The cells also contained UV-absorbing cytoplasmic compounds, with the extrachloroplastic carotenoid astaxanthin providing most of the screening. Additional screening compound(s) soluble in aqueous methanol with an absorption maximum at 335 nm played a minor role. Thus, cells are protected against potentially high levels of UV radiation by the snow itself when they live several centimeters beneath the surface, and they rely on cellular screening compounds, chiefly astaxanthin, when located near the surface where UV fluxes are high.
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PMID:Ultraviolet radiation and the snow alga Chlamydomonas nivalis (Bauer) Wille. 1287 Aug 46

By a functional expression screening with cyanobacterial cells, a new member of group 3 late embryogenesis abundant protein genes (designated cw80lea3) was isolated from the cDNA library of halotolerant green alga Chlamydomonas sp. strain W80. The principle of the screening method was based on the acquisition of NaCl salt-tolerance of the fresh water cyanobacterial cells carrying the halotolerant algal gene. The expression of cw80lea3 gene in the C. W80 cells was induced by salt- and cold-stresses, but not by abscisic acid treatment.
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PMID:Isolation of a new member of group 3 late embryogenesis abundant protein gene from a halotolerant green alga by a functional expression screening with cyanobacterial cells. 1521 88

Although cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241, exhibits a lower apparent molecular mass (34 kD) than that of the mesophile C. reinhardtii (41 kD) based on SDS-PAGE, both proteins are comparable in calculated molecular mass and show 79% identity in amino acid sequence. The difference in apparent molecular mass was maintained after expression of petA from both Chlamydomonas species in either E. coli or a C. reinhardtii DeltapetA mutant and after substitution of a unique third cysteine-292 to phenylalanine in the psychrophilic cytochrome f. Moreover, the heme of the psychrophilic form of cytochrome f was less stable upon heating than that of the mesophile. In contrast to C. raudensis, a C. reinhardtii DeltapetA mutant transformed with petA from C. raudensis exhibited the ability to undergo state transitions and a capacity for intersystem electron transport comparable to that of C. reinhardtii wild type. However, the C. reinhardtii petA transformants accumulated lower levels of cytochrome b ( 6 ) /f complexes and exhibited lower light saturated rates of O(2) evolution than C. reinhardtii wild type. We show that the presence of an altered form of cytochrome f in C. raudensis does not account for its inability to undergo state transitions or its impaired capacity for intersystem electron transport as previously suggested. A combined survey of the apparent molecular mass, thermal stability and amino acid sequences of cytochrome f from a broad range of mesophilic species shows unequivocally that the observed differences in cytochrome f structure are not related to psychrophilly. Thus, caution must be exercised in relating differences in amino acid sequence and thermal stability to adaptation to cold environments.
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PMID:Cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241: structure, sequence, and complementation in the mesophile, Chlamydomonas reinhardtii. 1642 16


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