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51.
Analysis of the ruv locus of Escherichia coli K-12 and identification of the gene product. 总被引:10,自引:5,他引:5
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The ruv gene of Escherichia coli, which is associated with inducible mechanisms of DNA repair and recombination, has been cloned into the low-copy plasmid vector pHSG415. The recombinant plasmid pPVA101 fully complements the DNA repair-deficient phenotype of ruv mutants. Restriction endonuclease analysis of this plasmid revealed a 10.6-kilobase (kb) HindIII DNA insert which contained a 7.7-kb PstI fragment identified as being from the chromosomal ruv region. Deletion analysis and Tn1000 insertional inactivation of ruv function located the ruv coding region to a 2.2-kb section of the cloned DNA fragment. A comparison of the proteins encoded by ruv wild-type and mutant plasmids identified the gene product as a protein of molecular weight 41,000. 相似文献
52.
Pruned source-sink transport systems from predarkened plants of Amaranthus caudatus L. and Gomphrena globosa L. were used to study the localization of 14C-labeled photosynthate imported into experimentally induced sink leaves by microautoradiography. During a 6-h (Amaranthus) or a 4-h (Gomphrena) transport period, 14C-assimilates were translocated acropetally from a mature source leaf provided with 14CO2, into a younger induced sink leaf (dark/-CO2). In addition, a young still-expanding source leaf exposed to 14CO2 exported 14C-assimilates basipetally into a mature induced sink leaf (dark/-CO2). Microautoradiographs showed that imported 14C-photosynthate was strongly accumulated in the sieve element/companion cell complexes of midveins, secondary veins, and minor veins of both the mature and the expanding sink leaf. Some label was also present in the vascular parenchyma and bundlesheath cells. In petioles, 14C-label was concentrated in the sieve element/companion cell complexes of all bundles indicating that assimilates were imported and distributed via the phloem. Moreover, a considerable amount of radioactivity unloaded from the sieve element/companion cell complexes of petiolar bundles, was densely located at sites of secondary wall thickenings of differen-tiating metaxylem vessels, and at sites of chloroplasts of the vascular parenchyma and bundle-sheath cells. These observations were more striking in petioles of Gomphrena than Amaranthus.Abbreviation se/cc
sieve element/companion cell 相似文献
53.
Butyrate formation from glucose by the rumen protozoon Dasytricha ruminantium. 总被引:2,自引:0,他引:2
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Production of butyrate by the holotrich protozoon Dasytricha ruminantium involves the enzymes of glycolysis, pyruvate:ferredoxin oxidoreductase, acetyl-CoA:acetyl-CoA C-acetyltransferase, 3-hydroxybutyryl-CoA dehydrogenase, 3-hydroxyacyl-CoA hydro-lyase, 3-hydroxyacyl-CoA reductase, phosphate butyryltransferase and butyrate kinase. Subcellular fractionation by differential and density-gradient centrifugation on sucrose gradients indicated that all those enzymes except pyruvate:ferredoxin oxidoreductase were non-sedimentable at 6 X 10(6) g-min. Butyrate kinase and phosphate butyryltransferase were associated with the large- and small-granule fractions. Thus, although metabolic reactions necessary for butyrate production proceed predominantly in the cytosol, hydrogenosomes play a key role in the conversion of pyruvate into acetyl-CoA. 相似文献
54.
Human glyceraldehyde-3-phosphate dehydrogenase: mRNA levels and enzyme activity in developing muscle. 总被引:3,自引:1,他引:2
Analysis of human glyceraldehyde-3-phosphate dehydrogenase mRNA revealed that levels in adult skeletal muscle are 12-fold greater per microgram of polyadenylated RNA than in fetal skeletal muscle, whereas in cardiac muscle RNA levels were about equal in fetal and adult tissue. The mRNA levels correlate well with glyceraldehyde 3-phosphate dehydrogenase enzyme activities. There was no evidence for fetus- or tissue-specific forms. 相似文献
55.
We have studied the activities of 2′,3′-cyclic nucleotide 3′-phosphohydrolase, 1,2-diacylglycerol: CDPethanolamine phosphoethanolamine
transferase (EC 2.7.8.1), and 1,2-diacylglycerol: CDPcholine phosphocholine transferase (EC 2.7.8.2) in developing rat brain
gray matter and white matter. The specific activity of cyclic nucleotide phosphohydrolase was 5–8 fold higher in white matter
than in gray matter at all ages. No significant changes were observed during development. The specific activity of phosphocholine
transferase was 2 to 3 fold higher than phosphoethanolamine transferase at all ages both in gray and white matter. Both phosphocholine
transferase and phosphoethanolamine transferase increased more than 2 fold in specific activity between 14 and 90 days of
age. The total activity of phosphocholine transferase also showed an increase during development. The apparentK
m values for nucleotides and dicaprin were similar in gray matter and white matter. Except for lowK
m values for nucleotides at 14 days of age, no significant changes were observed during development. Changes in rates of glycerophospholipid
synthesis may be partly due to the specific activities of these enzymes but are also determined by the quantities of substrates
and inhibitors and by affinities for the substrates.
Special Issue dedicated to Dr. Eugene Kreps. 相似文献
56.
Cortical microtubules wind around plant cells describing flat, medium or steeply pitched helices. Experiments now suggest that these arrays are dynamically interconvertible — providing a spring-like device that is sensitive to environmental cues and shifts the axis of cell expansion through 90°. 相似文献
57.
Genetic analysis and molecular cloning of the Escherichia coli ruv gene 总被引:22,自引:0,他引:22
Claire E. Shurvinton Robert G. Lloyd Fiona E. Benson Paul V. Attfield 《Molecular & general genetics : MGG》1984,194(1-2):322-329
Summary The genetic organisation of the ruv gene, a component of the SOS system for DNA repair and recombination in Escherichia coli, was investigated. New point mutations as well as insertions and deletions were generated using transposon Tn10 inserted in eda as a linked marker for site specific mutagenesis, or directly as a mutagen. The mutations were ordered with respect to one another and previously isolated ruv alleles by means of transductional crosses. The direction of chromosome mobilization from ruv:: Mud(ApR
lac)strains carrying F42lac
+ established that ruv is transcribed in a counterclockwise direction. Recombinant phages able to restore UV resistance to ruv mutants were identified, and the ruv
+ region was subcloned into a low copy number plasmid. The ruv
+ plasmid was able to correct the extreme radiation sensitivity and recombination deficiency of ruv recBC sbcB strains. 相似文献
58.
Lloyd A. Greene P. John Seeley Adriana Rukenstein Margaret DiPiazza rew Howard 《Journal of neurochemistry》1984,42(6):1728-1734
Abstract: Nerve growth factor protein (NGF) was found to rapidly promote the activation of tyrosine hydroxylase in cultured rat PC 12 pheochromocytoma cells. PC 12 cultures were exposed to NGF for periods of less than 1 h and the soluble contents of homogenates prepared from the cells were assayed for tyrosine hydroxylase activity. Under these conditions, the specific enzymatic activity was increased by 60 ± 10% (n = 13) in comparison with that in untreated sister cultures. The increase was half maximal by 2–5 min of exposure and at NGF concentrations of about 10 ng/ml (0.36 n M ). Antiserum against NGF blocked the effect. Tyrosine hydroxylase activity could also be rapidly increased by NGF in cultures of PC12 cells that had been treated with the factor for several weeks in order to produce a neuron-like phenotype. This was achieved by withdrawing NGF for about 4 h and then readding it for 30 min. The NGF-induced increase of tyrosine hydroxylase activity in PC12 cultures was not affected by inhibition of protein synthesis and therefore appeared to be due to activation of the enzyme. Kinetic experiments revealed that NGF brought about no change in the apparent Km of the enzyme for tyrosine or for co-factor (6-methyltetrahydropteridine), but that it did significantly increase the apparent maximum specific activity of the enzyme. These observations suggest that NGF (perhaps released by target organs) could promote a rapid and local enhancement of noradrenergic transmission in the sympathetic nervous system. 相似文献
59.
Native unploughed tallgrass prairie from Konza Prairie, Kansas, USA is described with respect to plant species compositional changes over a five year period in response to fire and topography. The principal gradient of variation in the vegetation is related to time since burning. Species show an individualistic response in terms of relative abundance to this gradient. Both the percentage of and cover of C4 species and all grasses decrease as the prairie remains unburnt. Forb and woody plant species numbers and abundance increase along this gradient. A secondary gradient of variation reflects topography (i.e. upland versus lowland soils). Upland soils support a higher species richness and diversity. Upland and lowland plant assemblages are distinct except on annually burnt prairie. The interaction between burning regime, topography and year-to-year climatic variation affects the relative abundance of the plant species differentially. The most dominant species overall, Andropogon gerardii, was affected only by year-to-year variation (i.e. climate). Its position at the top of the species abundance hierarchy was unaffected by burning regime or soil type. The other dominant species showed a suite of varying responses to these factors.Deceased May, 1986. 相似文献
60.
Abstract A mass spectrometer with membrane inlet was used to study methanol metabolism by Methanosarcina barkeri strain MS. The addition of methanol to methanol grown culture samples in the mass spectrometer vessel stimulated methanogenesis and hydrogen production. The apparent K s for methanol was determined as 0.5 mM and the V max as 8.14 mmol g (dry weight) h−1 . The V max for methane production was fairly constant during growth of the culture on methanol implying that growth is tightly coupled to methanogenesis. The addition of methanol to culture samples in the mass spectrometer vessel stimulated methanogenesis with no lag which indicated that methanogenesis can be uncoupled from growth. Exposure of the culture sample in the mass spectrometer vessel to an atmosphere of 2 kPa oxygen for 80 min resulted in a decrease in the rate of methanogenesis from methanol but on returning the atmosphere to nitrogen the addition of further methanol stimulated methanogenesis. The effect of other inhibitors of methanogenesis (2-bromoethane sulphonate and monensin); K j values 21.5 μM and 0.3 mM, respectively) were also studied. 相似文献