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211.
The cell content of substances (proteins, nucleic acids and chlorophylls) which play a significant role in growth processes in algae was used to characterize the physiological state of a continuous culture ofChlorella pyrenoidosa. The ratio of the various components of the cell content did not alter significantly with changes in the dilution rate. An increase in the mean cell volume was accompanied by a proportional increase in the amount of the various components. Their respective dry weight concentrations rose with the dilution rate and after reaching a maximum either fell or remained constant. The specific rates of synthesis of the given substances tended to rise, i.e. maximum activity of the culture was not attained. Deoxyribonucleic acid synthesis appears to be the endogenous factor limiting growth of the culture. The proportion of the individual nucleic acid fractions was compared with protein synthesis. 相似文献
212.
axl, a transforming gene isolated from primary human myeloid leukemia cells, encodes a novel receptor tyrosine kinase. 总被引:14,自引:0,他引:14
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J P O'Bryan R A Frye P C Cogswell A Neubauer B Kitch C Prokop R Espinosa rd M M Le Beau H S Earp E T Liu 《Molecular and cellular biology》1991,11(10):5016-5031
Using a sensitive transfection-tumorigenicity assay, we have isolated a novel transforming gene from the DNA of two patients with chronic myelogenous leukemia. Sequence analysis indicates that the product of this gene, axl, is a receptor tyrosine kinase. Overexpression of axl cDNA in NIH 3T3 cells induces neoplastic transformation with the concomitant appearance of a 140-kDa axl tyrosine-phosphorylated protein. Expression of axl cDNA in the baculovirus system results in the expression of the appropriate recombinant protein that is recognized by antiphosphotyrosine antibodies, confirming that the axl protein is a tyrosine kinase. The juxtaposition of fibronectin type III and immunoglobulinlike repeats in the extracellular domain, as well as distinct amino acid sequences in the kinase domain, indicate that the axl protein represents a novel subclass of receptor tyrosine kinases. 相似文献
213.
To study the activity of the epidermal growth factor (EGF) receptor during EGF-directed internalization, liver epithelial cells were exposed to EGF at 37 degrees C for various periods of time, washed, and homogenized at 0 degrees C. EGF receptor autophosphorylation was assessed in homogenates using [gamma-32P]ATP. Autophosphorylation was stimulated 3- to 6-fold in homogenates of cells incubated with EGF (100 ng/ml) for 15 min but was at or below basal levels in homogenates of cells treated with EGF for 2.5-5 min. This was surprising because immunoblotting revealed that EGF receptor phosphotyrosine (P-Tyr) content in intact cells was near maximal from 30 s to 5 min after EGF treatment. Excess EGF (1 microgram/ml), added after homogenization but prior to the assay, increased autophosphorylation in homogenates of cells that had not been treated with EGF, but failed to increase activity in homogenates of cells treated with EGF in culture for 2.5-5 min. Suppression of tyrosine phosphorylation of an exogenous kinase substrate was also observed at times paralleling the suppression of EGF receptor autophosphorylation. The transient suppression of receptor autophosphorylation in the cell-free assay was not explained by persistent occupation of autophosphorylation sites by phosphate added in the intact cells. The sites were greater than 80% dephosphorylated during the homogenization. Additionally phosphatase inhibition that prevented the normal loss of EGF receptor P-Tyr in intact cells at 15 min did not affect the pattern of early (2.5-5 min) suppression and later (15 min) stimulation of autophosphorylation measured in the cell-free assay. The suppression was not explained by activation of protein kinase C in that depletion of greater than 95% of cellular protein kinase C activity by an 18-h incubation of cells with 10 microM 12-O-tetradecanoylphorbol 13-acetate (TPA) did not affect the early suppression of autophosphorylation in EGF-treated cells. Moreover, under the conditions tested, activation of protein kinase C by short-term treatment (0.5-10 min) with TPA or angiotensin II did not appreciably alter subsequent autophosphorylation in the cell-free assay. In contrast, a 30 degrees C preincubation of homogenates from cells with suppressed EGF receptor autophosphorylation led to the recovery of the ability of EGF to stimulate EGF receptor autophosphorylation. These results suggest that a rapid reversible protein kinase C-independent process prevents detection of EGF receptor kinase activity during an early phase of EGF-dependent receptor internalization. 相似文献
214.
215.
Pavel Dvorak David Bednar Pavel Vanacek Lukas Balek Livia Eiselleova Veronika Stepankova Eva Sebestova Michaela Kunova Bosakova Zaneta Konecna Stanislav Mazurenko Antonin Kunka Tereza Vanova Karolina Zoufalova Radka Chaloupkova Jan Brezovsky Pavel Krejci Zbynek Prokop Petr Dvorak Jiri Damborsky 《Biotechnology and bioengineering》2018,115(4):i-i
216.
Molecular evolution of chloroplast DNA sequences 总被引:13,自引:1,他引:12
Comparative data on the evolution of chloroplast genes are reviewed. The
chloroplast genome has maintained a similar structural organization over
most plant taxa so far examined. Comparisons of nucleotide sequence
divergence among chloroplast genes reveals marked similarity across the
plant kingdom and beyond to the cyanobacteria (blue-green algae). Estimates
of rates of nucleotide substitution indicate a synonymous rate of 1.1 x
10(-9) substitutions per site per year. Noncoding regions also appear to be
constrained in their evolution, although addition/deletion events are
common. There have also been evolutionary changes in the distribution of
introns in chloroplast encoded genes. Relative to mammalian mitochondrial
DNA, the chloroplast genome evolves at a conservative rate.
相似文献
217.
High nucleotide sequence variation in a region of low recombination in Drosophila simulans is consistent with the background selection model 总被引:2,自引:0,他引:2
We surveyed nucleotide sequence variation at glucose dehydrogenase (Gld),
in a region of low recombination on chromosome 3R, from a population sample
of Drosophila simulans. The levels of nucleotide variation were
surprisingly high. There was no departure from the expectation of a neutral
model for the level of polymorphism, indicating no evidence of a selective
sweep in this region. There was a significant deficiency of singleton
polymorphisms according to the Fu and Li test, although Tajima and Hudson,
Kreitman, and Aguade (HKA) tests do not provide evidence of a significant
elevation of variation due to balancing selection. Genetic map data for the
D. simulans third chromosome were used to calculate expected values of pi
for Gld under a current model of background selection, varying the values
for the parameter sh (selection coefficient against deleterious mutations).
We show that the recombinational landscape of D. simulans is sufficiently
different from that of D. melanogaster that we expect higher variation
under the background selection model, even when effective population sizes
are assumed to be equal. The data for Gld were tested against the
predictions using computer simulations of the distribution of the number of
segregating sites conditioned on pi. Background selection alone can explain
our observations as long as sh is larger than 0.005 and species-level
effective population size is assumed to be several- fold larger than in D.
melanogaster. Alternatively, the deleterious mutation rate may be smaller
in D. simulans, or balancing selection may be acting nearby, thereby
reducing the effect of background selection.
相似文献
218.
Comparative evolutionary analysis of rDNA ITS regions in Drosophila 总被引:17,自引:2,他引:15
Schlotterer C; Hauser MT; von Haeseler A; Tautz D 《Molecular biology and evolution》1994,11(3):513-522
The internal transcribed spacer (ITS) of the ribosomal DNA is generally
considered to be under low functional constraint, and it is therefore often
treated as a typical nonfunctional spacer sequence. We have analyzed the
ITS regions of five species from the Drosophila melanogaster subgroup, two
Drosophila species from outside this group (D. pseudoobscura and D.
virilis), as well as from the more distantly related dipteran fly Musca
domestica. The sequence comparisons show a distinctive
conservation/divergence pattern, indicating that some regions are more
conserved than others. Moreover, secondary-structure calculations indicate
several conserved structural elements within the ITS regions. On the other
hand, a statistical test that allows us to estimate the fraction of sites
that are not under selective constraint suggests that more than half of the
spacer is apparently free to diverge and evolves with a rate that is close
to the neutral rate of sequence evolution in Drosophila. The ITS sequences
can be used to derive a molecular phylogeny for the species under study. We
find that the ITS tree is largely in line with the so-far-known phylogeny
of this group of species, with one difference. The species most distant
within the D. melanogaster subgroup is D. yakuba, rather than D. orena, as
is normally assumed.
相似文献
219.
Water-based, biodegradable polyelectrolyte complex dispersions (PECs) prepared by mixing oppositely charged polyions are advantageous drug delivery systems due to constituent biocompatibility and nanoparticulate architectures. Reaction phase environmental parameters dictate PEC physicochemical properties, and specifically, complexation between polyelectrolytes having significantly different molecular weights leads to formation of water-insoluble aggregates. Starting with this fact, four-component similar and dissimilar molecular weight PEC chemistries were applied and compared with and without frequency-induced dispergation. The goal was to define nanoparticulate PEC systems with desirable characteristics for use in biological systems. Results show PEC formulations from precursors with similar low molecular weights yielded dispersions with suitable physicochemical characteristics, as verified by photon correlation spectroscopy and TEM, presumably due to efficient ion pairing. Similar low molecular weight PECs fabricated with dispergation exhibited pH-independent stability, as validated by charge and size measurements. These physicochemical advantages lead to an ideal delivery platform. 相似文献
220.
Monincová M Prokop Z Vévodová J Nagata Y Damborsky J 《Applied and environmental microbiology》2007,73(6):2005-2008
1,2,3-Trichloropropane (TCP) is a highly toxic and recalcitrant compound. Haloalkane dehalogenases are bacterial enzymes that catalyze the cleavage of a carbon-halogen bond in a wide range of organic halogenated compounds. Haloalkane dehalogenase LinB from Sphingobium japonicum UT26 has, for a long time, been considered inactive with TCP, since the reaction cannot be easily detected by conventional analytical methods. Here we demonstrate detection of the weak activity (k(cat) = 0.005 s(-1)) of LinB with TCP using X-ray crystallography and microcalorimetry. This observation makes LinB a useful starting material for the development of a new biocatalyst toward TCP by protein engineering. Microcalorimetry is proposed to be a universal method for the detection of weak enzymatic activities. Detection of these activities is becoming increasingly important for engineering novel biocatalysts using the scaffolds of proteins with promiscuous activities. 相似文献