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21.
Benoit Cousineau Fabrice Leclerc Robert Cedergren 《Journal of molecular evolution》1997,45(6):661-670
Sequence similarity has given rise to the proposal that IF-2, EF-G, and EF-Tu are related through a common ancestor. We evaluate
this proposition and whether the relationship can be extended to other factors of protein synthesis. Analysis of amino acid
sequence similarity gives statistical support for an evolutionary affiliation among IF-1, IF-2, IF-3, EF-Tu, EF-Ts, and EF-G
and suggests further that this association is a result of gene duplication/fusion events. In support of this mechanism, the
three-dimensional structures of IF-3, EF-Tu, and EF-G display a predictable domain structure and overall conformational similarity.
The model that we propose consists of three consecutives duplication/fusion events which would have taken place before the
divergence of the three superkingdoms: eubacteria, archaea, and eukaryotes. The root of this protein superfamily tree would
be an ancestor of the modern IF-1 gene sequence. The repeated fundamental motif of this protein superfamily is a small RNA
binding domain composed of two α-helices packed along side of an antiparallel β-sheet.
Received: 17 October 1996 / Accepted: 10 June 1997 相似文献
22.
L. Benoit C. Cailliez A. Gehin J. Thirion G. Raval H. Petitdemange 《Current microbiology》1995,30(5):305-312
The extracellular cellulase enzyme system of Clostridium A11 was fractionated by affinity chromatography on Avicel: 80% of the initial carboxymethylcellulase (CMCase) activity was adhered. This cellulase system was a multicomponent aggregate. Several CMCase activities were detected, but the major protein P1 had no detectable activity. Adhered and unadhered cellulases showed CMCase activity with the highest specific activity in Avicel-adhered fraction. However, only afhered fractions could degrade Avicel. Thus, efficiency of the enzymatic hydrolysis of Avicel was related to the cellulase-adhesion capacity. Carboxymethylcellulase and Avicelase activities were studied with the extracellular enzyme system and cloned cellulases. Genomic libraries from Clostridium A11 were constructed with DNA from this Clostridium, and a new gene cel1 was isolated. The gene(s) product(s) from cel1 exhibited CMCase and p-nitrophenylcellobiosidase (pNPCbase) activities. This cloned cellulase adhered to cellulose. Synergism between adhered enzyme system and cloned endoglucanases was observed on Avicel degradation. Conversely, no synergism was observed on CMC hydrolysis. Addition of cloned endoglucanase to cellulase complex led to increase of the Vmax without significant K
m
variation. Cloned endoglucanases can be added to cellulase complexes to efficiently hydrolyze cellulose. 相似文献
23.
High biological activity of the synthetic replicates of somatostatin-28 and somatostatin-25 总被引:4,自引:0,他引:4
Paul Brazeau Nicholas Ling Frederick Esch Peter Böhlen Robert Benoit Roger Guillemin 《Regulatory peptides》1981,1(4):255-264
We have isolated form extracts of ovine hypothalami two molecules characterized as somatostatin-28 and somatostatin-4-28 (referred to as somatostatin-25). They were reproduced by solid hase synthesis. In equimolar ratio and depending upon the experimental conditions, synthetic somatostatin-28 ans somatostatin-25 are 3-14 times more potent than somatostatin-14 to inhibit the basal in vitro secretion of growth hormone or as stimulated by prostaglandin (PGE2). In early studies in vivo, somatostatin-28 and somatostatin-25 are also more potent than somatostatin-14 in inhibiting the secretion of growth hormone acutely stimulated in the rat by injection of morphine; somatostatin-28 is also longer-acting than somatostatin-14. These results suggest that somatostatin-14, as originally isolated, is a biologically active fragment of a larger molecule of greater specific activity; it should be considered as another form of somatostatin with high biological activity present in some tissues and likely secreted y the tissues along with somatostatin-14 and possibly other somatostatin-peptides of diverse sizes. 相似文献
24.
Variations in aspartasic activity in various media are due to aspartate-ammonium lyase induction and to regulation of the biosynthesis of this enzyme. Evidence for neosynthesis of the enzyme is provided by labelling and separation of the protein. The inducer appears to be aspartic acid. The biosynthesis is subject to pronounced catabolic repression. The physiological function of aspartate-ammonium lyase is discussed. 相似文献
25.
The aunting behavior in a captive group of 22 squirrel monkeys containing three infants was done in terms of the age/sex classification
of those animals involved. The time course of the aunting phenomena and the type and intensity of the interactions between
the mothers and the aunts were recorded. Males as well as females were observed to ascertain if the babysitters were sex specific.
Observations were gathered before, during, and after a particular threat to any monkey who was carrying an infant. Three categories
of protective behavior (protect, retreat, and nothing) were tabulated. The results indicated that most aunting and protection
occurred between infant ages 2-1/2-5 weeks when the infants were growing rapidly but not as yet socially self-sufficient.
Mothers protected infants the most against juveniles, then subadult males, and least against other adult females. Subadult
males were occasionally observed to carry and protect older infants. Aunting behavior was discussed in terms of the selective
pressures by which it may have evolved. 相似文献
26.
Preparation and biological properties of native and recombinant ciliary neurotrophic factor. 总被引:1,自引:0,他引:1
S K Gupta M Altares R Benoit R J Riopelle R J Dunn P M Richardson 《Journal of neurobiology》1992,23(5):481-490
CNTF (ciliary neurotrophic factor), purified from rabbit sciatic nerves by a relatively simple procedure, is bioactive in tissue culture at low picomolar concentration and appears as a doublet on polyacrylamide gel electrophoresis (PAGE). In these nerves, CNTF accounts for more than one-half of the survival-promoting activity on ciliary neurons. The concentration of CNTF in rabbit sciatic nerves is estimated to be 5 nmol/kg, more than 1000 times higher than would seem to be required to support neurons if the neurotrophic factor were homogeneously distributed. With recombinant DNA technology, rat CNTF has been synthesized in Escherichia coli, purified without denaturating agents, and found to be bioactive at a slightly lower concentration than CNTF extracted from rabbit sciatic nerves. After radioiodination, CNTF retains biological activity but is not specifically internalized and retrogradely transported in motor and sensory axons. In peripheral nerves, ciliary neurotrophic factor differs biologically from nerve growth factor (NGF) by its much higher tissue concentration and apparent lack of internalization by peripheral nerve axons. 相似文献
27.
Judith A. Siuciak Paul H. Gamache Margarita L. Dubocovich 《Journal of neurochemistry》1992,58(2):722-729
Levels of norepinephrine, epinephrine, dopamine, and serotonin (5-HT) and their precursors [tyrosine, L-3,4-dihydroxyphenylalanine, tryptophan, and 5-hydroxytryptophan (5-HTP)] and metabolites [3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), homovanillic acid, 3-methoxy-4-hydroxyphenylglycol, and 5-hydroxyindoleacetic acid (5-HIAA)] were determined concurrently in samples of chick retina, pineal gland, and nine selected areas of the brain (optic lobes, thalamus, hypothalamus, optic chiasm, pons/medulla, cerebellum, neostriatum/ectostriatum, hyperstriatum, and basal forebrain) using HPLC coupled with a coulometric electrode array detection system. The norepinephrine level was highest in the pineal gland, but it was also widely distributed throughout the chick brain, with the thalamus and hypothalamus showing substantial levels. The dopamine level was highest in the basal forebrain. The epinephrine level was highest in the hypothalamus. The thalamus and hypothalamus showed the highest levels of 5-HT. Daytime levels (1100 h) of these compounds were compared with levels in chicks killed in the middle of the dark phase (2300 h). In the brain areas examined, no day/night variations in levels of norepinephrine, epinephrine, dopamine, or 5-HT were seen, although significant nocturnal changes in levels of their metabolites were observed in some areas. Pineal levels of 5-HIAA decreased significantly at night. The retina showed significant nocturnal increases in 5-HTP, 5-HT, and 5-HIAA levels. Retinal levels of 3-MT and DOPAC were significantly decreased at night. 相似文献
28.
Spores and vegetative cells of Bacillus thuringiensis were more sensitive to UV light than were spores or cells of plasmid-cured B. thuringiensis strains or of the closely related Bacillus cereus. Introduction of B. thuringiensis plasmids into B. cereus by cell mating increased the UV sensitivity of the cells and spores. Protoxins encoded by one or more B. thuringiensis plasmids were not involved in spore sensitivity, since a B. thuringiensis strain conditional for protoxin accumulation was equally sensitive at the permissive and nonpermissive temperatures. In addition, introduction of either a cloned protoxin gene, the cloning vector, or another plasmid not containing a protoxin gene into a plasmid-cured strain of B. thuringiensis all increased the UV sensitivity of the spores. Although the variety of small, acid-soluble proteins was the same in the spores of all strains examined, the quantity of dipicolinic acid was about twice as high in the plasmid-containing strains, and this may account for the differences in UV sensitivity of the spores. The cells of some strains harboring only B. thuringiensis plasmids were much more sensitive than cells of any of the other strains, and the differences were much greater than observed with spores. 相似文献
29.
S Lavielle N Ling P Brazeau R Benoit T Wasada D Harris R Unger R Guillemin 《Biochemical and biophysical research communications》1979,91(2):614-622
The synthesis by solid-phase methodology of two glycosylated analogs of somatostatin [Glc-Asn5]-SS and [NAcGlc-Asn5]-SS is described. These two analogs have been biologically tested on the secretion of pituitary growth hormone, pancreatic glucagon and insulin. The results show that glycosylation of somatostatin on the Asn5 residue decreases by a hundred fold the inhibition activity on GH release when tested . , since the activity is similar to somatostatin the carbohydrates are probably removed by some enzymatic reaction and thus liberate the full activity of somatostatin. 相似文献
30.
Rapid enumeration of Fecal Coliforms in water by a colorimetric beta-galactosidase assay. 总被引:8,自引:7,他引:1
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The colorimetric beta-galactosidase assay is based upon the enzymatic hydrolysis of the substrate o-nitrophenyl-beta-D-galactoside (ONPG) by fecal coliforms. This technique provides an estimate of the fecal coliform concentration within 8 to 20 h. A 100-ml portion of test sample was passed through a 0.45 micrometer membrane filter. This filter was then incubated at 37 degrees C for 1 h in EC medium followed by the addition of filter-sterilized ONPG. The incubation was continued at 44.5 degrees C until a half-maximum absorbance (at 420 nm) was reached. The time between the start of incubation and the half-maximum absorbance was proportional to the concentration of fecal coliforms present. Escherichia coli (K-12) was used to measure the kinetics of substrate hydrolysis and the response time of different cell concentrations. High cell densities produced an immediate response, whereas 1 cell/ml will produce a response in less than 20 h. In field studies in which samples were taken from a range of grossly polluted streams to relatively clean lake water, a linear correlation between ONPG hydrolysis times and fecal coliform most-probable-number values was established. A total of 302 isolates randomly selected from positive ONPG-EC media, which were derived from 11 different habitats, were identified as E. coli (96.69 percent), Enterobacter cloacae (2.32 percent), Klebsiella pneumoniae (0.66 percent), and Citrobacter freundii (0.33 percent). 相似文献