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271.
Cloning of a human tRNA isopentenyl transferase 总被引:2,自引:0,他引:2
A cDNA of human origin is shown to encode a tRNA isopentenyl transferase (E.C. 2.5.1.8). Expression of the gene in a Saccharomyces cerevisiae mutant lacking the endogenous tRNA isopentenyl transferase MOD5 resulted in functional complementation and reintroduction of isopentenyladenosine into tRNA. The deduced amino acid sequence contains a number of regions conserved in known tRNA isopentenyl transferases. The similarity to the S. cerevisiae MOD5 protein is 53%, and to the Escherichia coli MiaA protein 47%. The human sequence was found to contain a single C2H2 Zn-finger-like motif, which was detected also in the MOD5 protein, and several putative tRNA transferases located by BLAST searches, but not in prokaryotic homologues. 相似文献
272.
Kari Lehtilä 《Evolutionary ecology》2000,14(4-6):315-330
Many plants show compensatory regrowth after herbivory and dormant buds often have an important role in compensatory responses.
Theoretical models have shown that herbivore damage may select for a bud bank, i.e., a pool of dormant buds that are protected
from herbivory and that are activated after herbivore damage. Earlier models assumed that undamaged plants cannot activate
their dormant buds without damage, although they apparently have sufficient resources for successful seed production through
the additional shoots dormant buds could produce. However, many plants are able to gradually activate buds over an extended
period of time without any cue from damage. The aim of this study was to analyze how herbivory imposes selection for gradual
mobilization of the bud bank. I assume that selection pressures that affect the fraction of buds active at each time point
include damage by herbivores, time left to the end of season, and the opportunity costs of dormant buds. I modelled bud dynamics
with gradual activation when there is a single damage event and (i) when the seed set of a shoot is not dependent on the time
it is active, or (ii) when the seed set of a shoot diminishes with later activation. In addition, I analyzed how (iii) risk
of repeated herbivory affects selection for gradual activation. Under these models, gradual activation is optimal over a wide
range of herbivory pressures. Selection appears to favour activation of all buds at the beginning of the season only when
herbivore pressure is weak and when early shoots have a higher seed set than late shoots. Alternatively, strong herbivore
pressure and late damage may select for a large bud bank throughout the growing season, without gradual activation; the bud
bank is only mobilized after damage. In this case, damaged plants can overcompensate, i.e. they have a higher seed set than
undamaged plants with the same bud activation pattern. Selection for overcompensation demands a stronger herbivore pressure
in this current model than in earlier bud bank models. The model never predicts selection for overcompensation when there
is a risk of repeated herbivory.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
273.
Lysyl hydroxylase is the enzyme catalyzing the formation of hydroxylysyl residues in collagens. Large differences in the extent of hydroxylysyl residues are found among collagen types. Three lysyl hydroxylase isoenzymes (LH1, LH2, LH3) have recently been characterized from human and mouse tissues. Nothing is known about the distribution of these isoforms within cells or whether they exhibit collagen type specificity. We measured mRNA levels of the three isoforms, as well as the mRNAs of the main collagen types I, III, IV, and V and the alpha subunit of prolyl 4-hydroxylase, another enzyme involved in collagen biosynthesis, in different human cell lines. Large variations were found in mRNA expression of LH1 and LH2 but not LH3. Immunoblotting was utilized to confirm the results of Northern hybridization. The levels of mRNA of LH1, LH2, and the alpha subunit of prolyl 4-hydroxylase showed significant correlations with each other. The LH3 mRNA levels did not correlate with those of LH1, LH2, or the alpa subunit of prolyl 4-hydroxylase, clearly indicating a difference in the regulation of LH3. No correlation was observed between LH isoforms and individual collagen types, indicating a lack of collagen type specificity for lysyl hydroxylase isoforms. Our observations suggest that LH1, LH2, and the alpha subunit of prolyl 4-hydroxylase are coregulated together with total collagen synthesis but not with the specific collagen types and indicate that LH3 behaves differently from LH1 and LH2, implying a difference in their substrates. These observations set the basis for further studies to define the functions of lysyl hydroxylase isoforms. 相似文献
274.
Susanne Siebentritt Enrico Avancini Marcus Br Jakob Bombsch Emilie Bourgeois Stephan Buecheler Romain Carron Celia Castro Sebastien Duguay Roberto Flix Evelyn Handick Dimitrios Hariskos Ville Havu Philip Jackson Hannu‐Pekka Komsa Thomas Kunze Maria Malitckaya Roberto Menozzi Milos Nesladek Nicoleta Nicoara Martti Puska Mohit Raghuwanshi Philippe Pareige Sascha Sadewasser Giovanna Sozzi Ayodhya Nath Tiwari Shigenori Ueda Arantxa Vilalta‐Clemente Thomas Paul Weiss Florian Werner Regan G. Wilks Wolfram Witte Max Hilaire Wolter 《Liver Transplantation》2020,10(8)
275.
Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.] 总被引:5,自引:0,他引:5
Summary Relationships between root zone temperature, concentrations and uptake rates of NH
4
+
and NO
3
–
were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH
4
+
and NO
3
–
uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (Cmin) range of 100–150 M uptake rates of NH
4
+
were 3–4 times higher than those of NO
3
–
The preference for NH
4
+
uptake was also reflected in the minimum concentration (Cmin) values. Supplying NH4NO3, the rate of NO
3
–
uptake was very low until the NH
4
+
concentrations had fallen below about 100 M. The shift from NH
4
+
to NO
3
–
uptake was correlated with a corresponding shift from net H+ production to net H+ consumption in the external solution. The uptake rates of NH
4
+
were correlated with equimolar net production of H+. With NO
3
–
nutrition net consumption of H+ was approximately twice as high as uptake rates of NO
3
–
In the forest stand the NO
3
–
concentration in the soil solution was more than 10 times higher than the NH
4
+
concentration (<100 M), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO
3
–
uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium. 相似文献
276.
Schaller J Brackhage C Gessner MO Bäuker E Gert Dudel E 《Plant biology (Stuttgart, Germany)》2012,14(2):392-396
Silicon is a non-essential element for plant growth. Nevertheless, it affects plant stress resistance and in some plants, such as grasses, it may substitute carbon (C) compounds in cell walls, thereby influencing C allocation patterns and biomass production. How variation in silicon supply over a narrow range affects nitrogen (N) and phosphorus (P) uptake by plants has also been investigated in some detail. However, little is known about effects on the stoichiometric relationships between C, N and P when silicon supply varies over a broader range. Here, we assessed the effect of silicon on aboveground biomass production and C:N:P stoichiometry of common reed, Phragmites australis, in a pot experiment in which three widely differing levels of silicon were supplied. Scanning electron microscopy (SEM) showed that elevated silicon supply promoted silica deposition in the epidermis of Phragmites leaves. This resulted in altered N:P ratios, whereas C:N ratios changed only slightly. Plant growth was slightly (but not significantly) enhanced at intermediate silicon supply levels but significantly decreased at high levels. These findings point to the potential of silicon to impact plant growth and elemental stoichiometry and, by extension, to affect biogeochemical cycles in ecosystems dominated by Phragmites and other grasses and sedges. 相似文献
277.
Ahlqvist KJ Hämäläinen RH Yatsuga S Uutela M Terzioglu M Götz A Forsström S Salven P Angers-Loustau A Kopra OH Tyynismaa H Larsson NG Wartiovaara K Prolla T Trifunovic A Suomalainen A 《Cell metabolism》2012,15(1):100-109
Somatic stem cell (SSC) dysfunction is typical for different progeroid phenotypes in mice with genomic DNA repair defects. MtDNA mutagenesis in mice with defective Polg exonuclease activity also leads to progeroid symptoms, by an unknown mechanism. We found that Polg-Mutator mice had neural (NSC) and hematopoietic progenitor (HPC) dysfunction already from embryogenesis. NSC self-renewal was decreased in vitro, and quiescent NSC amounts were reduced in vivo. HPCs showed abnormal lineage differentiation leading to anemia and lymphopenia. N-acetyl-L-cysteine treatment rescued both NSC and HPC abnormalities, suggesting that subtle ROS/redox changes, induced by mtDNA mutagenesis, modulate SSC function. Our results show that mtDNA mutagenesis affected SSC function early but manifested as respiratory chain deficiency in nondividing tissues in old age. Deletor mice, having mtDNA deletions in postmitotic cells and no progeria, had normal SSCs. We propose that SSC compartment is sensitive to mtDNA mutagenesis, and that mitochondrial dysfunction in SSCs can underlie progeroid manifestations. 相似文献
278.
M Johnsson I Gustafson CJ Rubin AS Sahlqvist KB Jonsson S Kerje O Ekwall O Kämpe L Andersson P Jensen D Wright 《PLoS genetics》2012,8(8):e1002914
Domestication is one of the strongest forms of short-term, directional selection. Although selection is typically only exerted on one or a few target traits, domestication can lead to numerous changes in many seemingly unrelated phenotypes. It is unknown whether such correlated responses are due to pleiotropy or linkage between separate genetic architectures. Using three separate intercrosses between wild and domestic chickens, a locus affecting comb mass (a sexual ornament in the chicken) and several fitness traits (primarily medullary bone allocation and fecundity) was identified. This locus contains two tightly-linked genes, BMP2 and HAO1, which together produce the range of pleiotropic effects seen. This study demonstrates the importance of pleiotropy (or extremely close linkage) in domestication. The nature of this pleiotropy also provides insights into how this sexual ornament could be maintained in wild populations. 相似文献
279.
Su Y Orelli B Madireddy A Niedernhofer LJ Schärer OD 《The Journal of biological chemistry》2012,287(26):21846-21855
ERCC1-XPF is a heterodimeric, structure-specific endonuclease that cleaves single-stranded/double-stranded DNA junctions and has roles in nucleotide excision repair (NER), interstrand crosslink (ICL) repair, homologous recombination, and possibly other pathways. In NER, ERCC1-XPF is recruited to DNA lesions by interaction with XPA and incises the DNA 5' to the lesion. We studied the role of the four C-terminal DNA binding domains in mediating NER activity and cleavage of model substrates. We found that mutations in the helix-hairpin-helix domain of ERCC1 and the nuclease domain of XPF abolished cleavage activity on model substrates. Interestingly, mutations in multiple DNA binding domains were needed to significantly diminish NER activity in vitro and in vivo, suggesting that interactions with proteins in the NER incision complex can compensate for some defects in DNA binding. Mutations in DNA binding domains of ERCC1-XPF render cells more sensitive to the crosslinking agent mitomycin C than to ultraviolet radiation, suggesting that the ICL repair function of ERCC1-XPF requires tighter substrate binding than NER. Our studies show that multiple domains of ERCC1-XPF contribute to substrate binding, and are consistent with models of NER suggesting that multiple weak protein-DNA and protein-protein interactions drive progression through the pathway. Our findings are discussed in the context of structural studies of individual domains of ERCC1-XPF and of its role in multiple DNA repair pathways. 相似文献
280.
Rembeck K Alsiö A Christensen PB Färkkilä M Langeland N Buhl MR Pedersen C Mørch K Westin J Lindh M Hellstrand K Norkrans G Lagging M 《PloS one》2012,7(1):e29370