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111.
RNA11 protein is associated with the yeast spliceosome and is localized in the periphery of the cell nucleus. 总被引:37,自引:14,他引:23
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T H Chang M W Clark A J Lustig M E Cusick J Abelson 《Molecular and cellular biology》1988,8(6):2379-2393
The yeast rna mutations (rna2 through rna10/11) are a set of temperature-sensitive mutations that result in the accumulation of pre-mRNAs at the nonpermissive temperature. Most of the yeast RNA gene products are involved in and essential for mRNA splicing in vitro, suggesting that they code for components of the splicing machinery. We tested this proposal by using an in vitro-synthesized RNA11 protein to complement the temperature-sensitive defect of the rna11 extract. During the in vitro complementation, the input RNA11 protein was associated with the 40S spliceosome and a 30S complex, suggesting that the RNA11 protein is indeed a component of the spliceosome. The formation of the RNA11-associated 30S complex did not require any exogenous RNA substrate, suggesting that this 30S particle is likely to be a preassembled complex involved in splicing. The RNA11-specific antibody inhibited the mRNA splicing in vitro, confirming the essential role of the RNA11 protein in mRNA splicing. Finally, using the anti-RNA11 antibody, we localized the RNA11 protein to the periphery of the yeast nucleus. 相似文献
112.
Transformation of Tetrahymena thermophila with hypermethylated rRNA genes. 总被引:5,自引:3,他引:2
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The extrachromosomal rRNA genes (rDNA) of Tetrahymena thermophila contain 0.4% N6-methyladenine. C3 strain rDNA was isolated, hypermethylated in vitro, and microinjected into B strain host cells. Clonal cell lines were established, and transformants were selected on the basis of resistance to paromomycin, conferred by the injected rDNA. The effects of methylation by three enzymes which methylate the sequence 5'-NAT-3', the dam, EcoRI, and ClaI methylases, were tested. Hypermethylation of the injected rDNA had no effect on transformation efficiency relative to mock-methylated controls. The injected C3 strain rDNA efficiently replaced host rDNA as the major constituent of the population of rDNA molecules. Hypermethylation of the injected DNA was not maintained through 20 to 25 cell generations. 相似文献
113.
114.
The N-terminal -amino groups of 1-bungarotoxin (1-Bgt) fromBungarus multicinctus venom were modified with trinitrobenzene sulfonic acid and the modified derivative was separated by high performance liquid chromatography. The trinitrophenylated (TNP) derivative contained two TNP groups at the -amino groups of A chain and B chain and showed a marked decrease in enzymatic activity. Methionine residues at positions 6 and 8 of the A chain were oxidized with chloramine T or cleaved with cyanogen bromide to remove the N-terminal octapeptide. Oxidation of methionine residues and removal of the N-terminal octapeptide caused a precipitous decrease in enzymatic activity, whereas antigenicity remained unchanged. The presence of dihexanoyllecithin influenced the interaction between 1-Bgt and 8-antilinonaphthalene sulfonate (ANS) and revealed that 1-Bgt consists of two types of ANS-binding sites, one at the substrate binding site of the A chain and the other might be at the B chain. The modified derivatives still retained their affinity for Ca2+ and ANS, indicating that the N-terminal region is not involved in Ca2+ and substrate binding. A fluorescence study revealed that the -amino group of the A chain was in the vicinity of substrate binding site and that the TNP -amino groups were in proximity to Trp-19 of the A chain. In addition, the study showed that the N-terminal region is important for stabilizing the architectural environment of Trp-19. The results, together with the proposal that Trp-19 of the A chain is involved in substrate binding, suggest that the N-terminal region of the A chain plays a crucial role in maintaining a functional active site for 1-Bgt. 相似文献
115.
116.
The utilization of amino acids for growth and their effects on nitrogen fixation differ greatly among the several strains of each species of Azospirillum spp. that were examined. A. brasiliense grew poorly or not at all on glutamate, aspartate, serine, or histidine as the sole nitrogen and carbon sources. Nitrogen fixation by most A. brasiliense strains was inhibited only slightly even by 10 mM concentrations of these amino acids. In contrast, A. lipoferum and A. amazonense grew very well on glutamate, aspartate, serine, or histidine as the sole nitrogen and carbon sources; nitrogen fixation, which was measured in the presence of malate or sucrose, was severely inhibited by these amino acids. It was concluded that growth on histidine as the sole source of nitrogen, carbon, and energy may be used for the taxonomic characterization of Azospirillum spp. and for the selective isolation of A. lipoferum. The different utilization of various amino acids by Azospirillum spp. may be important for their establishment in the rhizosphere and for their associative nitrogen fixation with plants. The physiological basis for the different utilization of glutamate by Azospirillum spp. was investigated further. A. brasiliense and A. lipoferum exhibited a high affinity for glutamate uptake (Km values for uptake were 8 and 40 microM, respectively); the Vmax was 6 times higher in A. lipoferum than in A. brasiliense. At high substrate concentrations (10 mM), the nonsaturable component of glutamate uptake was most active in A. lipoferum and A. amazonense.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
117.
An in-vivo measurement and analysis of viscoelastic properties of the spinal cord of cats 总被引:6,自引:0,他引:6
An in-vivo experimental technique was employed to determine the linear and nonlinear characteristics of viscoelastic properties of the spinal cord of anesthetized cats. The stress relaxation and recovery curves were reproducible in a group of cat experiments. The data of linear viscoelastic properties were used to develop a power law model with Boltzmann's convolution integral. The model was capable of predicting a prolonged stress relaxation and recovery curve. For larger deformation, the results were quantified using a nonlinear analysis of viscoelastic response of the spinal cord under the uniaxial experiment. 相似文献
118.
Amos Banin Glenn C. Carle Sherwood Chang Lelia M. Coyne James B. Orenberg Thomas W. Scattergood 《Origins of life and evolution of the biosphere》1988,18(3):239-265
Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils. 相似文献
119.
Summary A simple method is proposed for calculating oxygen pentration depth in immobilized cells by assuming zero order kinetics in the presence of several external oxygen transport resistances. Calculations indicate that typical penetration depths of oxygen for immobilized microbial cells are in the range of 50–200 and those for immobilized or encapsulated animal and plant tissue culture are about 500–1000 . Based on calculations, oxygen transport in microencapsulation and microcarriers for tissue cultures are not transport-limited, but a slight limitation is expected for those in a hollow fiber reactor.Nomenclature as
specific area of a support (cm)
- Bi
Biot number
-
dimensionless
- Cb
oxygen concentration in the bulk liquid (mM)
-
C
b
C
b
*
-Ccr (mM)
- C
b
*
bulk oxygen concentration in equilibrium with air (mM)
- Ccr
critical oxygen concentration (mM)
- Cs
oxygen concentration in the solid phase (mM)
- dp
diameter or thickness of a support (cm)
- Deff
effective diffusivity of oxygen in the solid phase (cm2/s)
- km
membrane permeability of oxygen (cm/s)
- k
m
*
Deff/m
- kLaL
liquid phase mass transfer rate coefficient (1/s)
- ksas
solid phase mass transfer rate coefficient (1/s)
- (OUR)v
volumetric oxygen uptake rate (mmol O2/l)
- p
geometry parameter, p=0 for slab, p=1 for cylinder, p=2 for sphere
- Pd
oxygen penetration depth (cm)
-
P
d
oxygen penetration depth in the absence of external diffusion limitation (cm)
- Q
volumetric oxygen uptake rate,
(mmol O2/l·h)
-
specific oxygen uptake rate (mmol O2gm biomass (dry)·h)
- r
length coordinate (cm)
- rc
oxygen penetration depth for sphere (cm)
-
r
c
rc in the absence of external diffusion limitation (cm)
- r
c
*
oxygen penetration depth for cylinder (cm)
-
r
c
*
r
c
*
in the absence of external diffusion limitation (cm)
- rcom
combined mass transfer rate resistance (s)
- rd
location where Cs becomes zero or Ccr (cm)
- ri
radius of cylinder or sphere, half thickness of slab (cm)
- Usg
superficial gas velocity (cm/s)
- X
cell concentration (g/l)
Greek letters
Thiele modulus, dimensionless
- L, s
liquid and solid phase volume fraction, respectively, dimensionless
-
effectiveness factor
On sabbatical leave from KAIST, Seoul, Korea 相似文献
120.