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21.
Differential expression of two related amino acid transporters with differing substrate specificity in Arabidopsis thaliana 总被引:8,自引:3,他引:5
Marion Kwart Brigitte Hirner Sabine Hummel Wolf B. Frommer 《The Plant journal : for cell and molecular biology》1993,4(6):993-1002
A general amino acid permease cDNA ( AAP2 ) was isolated from Arabidopsis by complementation of a yeast mutant defective in citrulline uptake. Direct transport measurements in yeast show that the protein mediates uptake of l -[14 C]-citrulline and l -[14 C]-proline. Detailed analyses of the substrate specificity by competition studies demonstrate that all proteogenic amino acids are recognized by the carrier, including those that represent the major transport forms of reduced nitrogen in many species, i.e. glutamine, glutamate and asparagine. Thus, AAP2 is less selective as compared with AAP1 and transports basic amino acids such as histidine as shown by expression in a histidine transport-deficient yeast strain. The predicted polypeptide of 53 kDa is highly hydrophobic with 12 putative membrane-spanning regions and shows significant homologies to the Arabidopsis broad specificity permease AAP1, and a limited homology to bacterial branched chain amino acid transporters, but not to any other known proteins. Alterations in the charged residues as compared with AAP1 in four regions might be involved in the difference in selectivity towards basic amino acids. Both genes are highly expressed in developing pods indicating a role in supplying the developing seeds with reduced nitrogen. AAP2 is selectively expressed in the stem and might therefore play a role in xylem-to-phloem transfer of amino acids during seed filling. Furthermore in situ hybridization shows that both genes are expressed in the vascular system of cotyledons in developing seedlings. 相似文献
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Hummel Herman Bogaards Roelof Bek Tatiana Polishchuk Lennard Amiard-Triquet Claude Bachelet Guy Desprez Michel Strelkov Peter Sukhotin Alex Naumov Andrei Dahle Salve Denisenko Stanislav Gantsevich Michael Sokolov Kirill Wolf Lein de 《Hydrobiologia》1997,355(1-3):127-138
The stress sensitivity, determined in copper exposureexperiments and in survival in air tests, and thegenetic structure, measured by means of isoenzymeelectrophoresis, were assessed in populations of theBaltic clam Macoma balthica (L.) from itssouthern to its northern distribution limit, in orderto test the hypotheses that near the distributionlimit the clams would be more stress sensitive andwould have a lower genetic variability. Thepopulations in west and north Europe show a stronggenetic resemblance. The populations in the sub-ArcticWhite Sea are genetically slightly different, and showa low stress sensitivity. The populations in theArctic Pechora Sea are genetically very distant fromthe other populations, and show the lowest stresssensitivity. Near the southern distribution limit, inagreement with the hypotheses, genetic variability islow and stress sensitivity high. On the other hand, incontrast to expectation, near the northerndistribution limit, in the populations of the PechoraSea, the genetic variability was higher, thus notreduced, and the stress sensitivity was low comparedto all other populations. Yet, it remains a questionif such is due to gradual physiologicalacclimatization (and ongoing differential selection)or to genetic adaptation. 相似文献
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Nadine B. Carozzi Gregory W. Warren Nalini Desai Susan M. Jayne Richard Lotstein Douglas A. Rice Stephen Evola Michael G. Koziel 《Plant molecular biology》1992,20(3):539-548
Insecticidal transgenic tobacco plants containing a truncated Bacillus thuringiensis cryIA(b) crystal protein (ICP) gene expressed from the CaMV 35S promoter were analyzed for ICP gene expression under field and greenhouse conditions over the course of a growing season. We present new information on temporal and tissue-specific expression of a CaMV 35S/cryIA(b) gene. Levels of cryIA(b) protein and mRNA were compared in both homozygous and hemizygous lines throughout plant development. Levels of ICP mRNA and protein increased during plant development with a pronounced rise in expression at the time of flowering. Homozygous ICP lines produced higher levels of ICP than the corresponding hemizygous lines. ELISA analysis of different tissues in the tobacco plant showed ICP gene expression in most tissues with a predominance of ICP in older tissue. All transgenic ICP tobacco lines which were studied in the field and greenhouse contained 400 ng to 1 g ICP per gram fresh weight in leaves from the mid-section of the plant at flowering. The amounts of ICP produced by field lines were directly comparable to levels observed in greenhouse-grown plants. 相似文献
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A comparative biochemical study was performed on some strains ofCandida rhagii and on strains belonging to different subgroups ofCandida parapsilosis. Measurements of alcohol dehydrogenase activity, resistance to drugs and occurrence of an alternative pathway enabled us to confirm the classification between several subgroups within theC. parapsilosis species. 相似文献
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The 4-arsono-2-nitrophenyl chromophore can serve as a versatile spectrophotometric probe of the surface structure of proteins. Values of pK1' and pK2' for the arsonic acid ionizations are near 3 and 8, respectively, and the presence of nearby positive and negative charges produces substantial alterations in the spectral response of the probe. Changes in the extinction at the wavelength of maximum difference are 30-50% of the extinction coefficients, epsilonmax, for each ionization of the arsonic acid moiety. The titration of 41-(4-arsono-2-nitrophenyl)ribonuclease A indicates that the arsonate dianion binds near the active-site histidine residues. With protonation of a carboxylate side chain in the acidic region, presumably aspartic acid-121, the active site is disrupted. The 41-(4-arsono-2-nitrophenyl) group interacts to a greater degree with the histidine-119 side chain than it does with the histidine-12 residue. Interactions of uridine or 3'-cytidylic acid with the ligand-binding region of 41-(4-arsono-2-nitrophenyl) ribonuclease A modify the spectrophotometric response extensively. 3'-Cytidylic acid binds 41-(4-arsono-2-nitrophenyl) ribonuclease A with an affinity 300 times less than that for native ribonuclease A and 17 times lower than that for 41-(2,4-dinitrophenyl) ribonuclease A. The arsononitrophenyl chromophore is responsive to changes in the active site of ribonuclease A induced by such perturbants as ligand binding, chemical modification, and both acid and thermal denaturation. 相似文献
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