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41.
42.
A cellular cofactor facilitates efficient 3CD cleavage of the poliovirus P1 precursor. 总被引:5,自引:4,他引:1 下载免费PDF全文
The production of poliovirus capsid proteins from a capsid protein precursor (P1) is mediated by virus-encoded proteinase 3CD and involves a complicated set of proteinase-substrate interactions. In addition to substrate and enzymatic determinants required for this interaction, we describe a cellular cofactor, which facilitates 3CD recognition of the P1 precursor. Cellular cofactor activity is 3CD dependent and salt dependent. Our analysis shows that proteolytic cleavage of the P1 precursor at the VP0/VP3 cleavage site exhibits a greater dependency on the cellular cofactor than cleavage at the VP3/VP1 site. Such a greater dependency on cellular cofactor activity can be relieved (in part) by the substitution of an Ala residue for the Pro residue at the -4 position of the VP0/VP3 cleavage site. However, mutant viruses containing Pro-to-Ala substitutions at the -4 position of the VP0/VP3 site exhibit defects in viral growth. 相似文献
43.
A phenotypic host range alteration determines RD114 virus restriction in feline embryonic cells. 总被引:4,自引:4,他引:0 下载免费PDF全文
We have characterized the restriction mechanism for RD114 virus replication in embryonic feline cells (FeF). By comparing growth properties of the virus in FeF cells with its behavior in a fetal feline glial cell line (G355) permissive for RD114, we showed that both cell lines were readily infectible by virus grown in permissive cells and that no significant differences in viral integration or viral RNA expression could be detected. However, analysis of viral protein expression revealed differences in viral env gene processing in the two cell types. Envelope precursor pR85 was produced, but the expected processed gp70 product was detectable only in permissive (G355) cells. An envelope product of 85 kDa was packaged into virions produced by FeF cells, while virions produced by G355 cells contained the expected RD114 gp70. While the gp85 env-containing virions were infectious for permissive G355 cells, they were unable to infect FeF cells. The block to infection by the gp85-containing particles in FeF cells could be abrogated by treatment with the glycosylation inhibitor tunicamycin. Our results indicate that restriction of RD114 virus involves a novel mechanism dependent on two factors: altered glycosylation of the envelope to a gp85 form and an altered RD114 receptor in FeF cells. 相似文献
44.
OBJECTIVE--To compare intramuscular oxytocin alone and intramuscular oxytocin with ergometrine (Syntometrine) for their effect in reducing the risk of postpartum haemorrhage when both are used as part of the active management of the third stage of labour. DESIGN--Double blind, randomised controlled trial. SETTING--Two metropolitan teaching hospitals in Perth, Western Australia. SUBJECTS--All women who expected a vaginal birth during the period of the trial. Informed consent was obtained. MAIN OUTCOME MEASURES--Postpartum haemorrhage, nausea, vomiting, and increased blood pressure. RESULTS--3497 women were randomly allocated to receive oxytocin-ergometrine (n = 1730) or oxytocin (n = 1753). Rates of postpartum haemorrhage (> or = 500 ml or > or = 1000 ml) were similar in both arms (odds ratio 0.90 (0.82); 95% confidence interval 0.75 to 1.07 (0.59 to 1.14) at 500 ml (1000 ml) threshold). The use of oxytocin-ergometrine was associated with nausea, vomiting, and increased blood pressure. CONCLUSIONS--There are few advantages but several disadvantages for the routine use of oxytoxinergometrine when prophylactic active management of the third stage of labour is practised. Further investigation of dose-response for oxytocin may be warranted. 相似文献
45.
A simple technic is described to produce well spread gymnosperm chromosomes. Root tip meristems are digested with a pectinase:cellulase mixture to produce a cell suspension which then is squashed to yield flat, well spread chromosome complements that can be stained or used for in situ hybridization. 相似文献
46.
Regulated underexpression of the FliM protein of Escherichia coli and evidence for a location in the flagellar motor distinct from the MotA/MotB torque generators. 总被引:7,自引:6,他引:1 下载免费PDF全文
The FliM protein of Escherichia coli is essential for the assembly and function of flagella. Here, we report the effects of controlled low-level expression of FliM in a fliM null strain. Disruption of the fliM gene abolishes flagellation. Underexpression of FliM causes cells to produce comparatively few flagella, and most flagella built are defective, producing subnormal average torque and fluctuating rapidly in speed. The results imply that in a normal flagellar motor, multiple molecules of FliM are present and can function independently to some degree. The speed fluctuations indicate that stable operation requires most, possibly all, of the normal complement of FliM. Thus, the FliM subunits are not as fully independent as the motility proteins MotA and MotB characterized in earlier work, suggesting that FliM occupies a location in the motor distinct from the MotA/MotB torque generators. Several mutations in fliM previously reported to cause flagellar paralysis in Salmonella typhimurium (H. Sockett, S. Yamaguchi, M. Kihara, V.M. Irikura, and R. M. Macnab, J. Bacteriol. 174:793-806, 1992) were made and characterized in E. coli. These mutations did not cause flagellar paralysis in E. coli; their phenotypes were more complex and suggest that FliM is not directly involved in torque generation. 相似文献
47.
A double-antibody-sandwich, enzyme-linked immunosorbent assay was developed to detect an extracellular proteinase produced by Pseudomonas fragi. The method was capable of detecting 4 g/ml of the proteinase in spiked samples of buffer and broth and 4.2 g/ml in a broth culture of the organism. The assay detected the presence of proteinase at bacterial densities of approximately 104 cfu/ml, which develop after incubation for 15 h at 25°C in a broth medium. All assays could be completed within 7 h. This assay is of value in plotting proteolytic expression in relation to the growth cycle of Ps. fragi in broth culture and may be of value, with development, in other more complex milieux. 相似文献
48.
Bruce R. Mate Kelly A. Rossbach Sharon L. Nieukirk Randall S. Wells A. Blair Irvine Michael D. Scott Andrew J. Read 《Marine Mammal Science》1995,11(4):452-463
An adult, female bottlenose dolphin ( Tursiops trucncatus ) was radio tagged and monitored via satellite-based Argos receivers for 25 d from 28 June to 23 July 1990, in Tampa Bay, Florida. A total of 794 transmissions were obtained during 106 satellite passes. A mean of 3.9 (SE = 0.24) locations/day were determined by Service Argos and showed the animal remained in the bay, usually close to the southeastern shore. The dolphin moved at least 581 km at a minimum mean speed of 1.2 (SE = 0.1) km/h. Data from 63, 922 dives were recorded. The animal spent an average of 87.1 (SE = 0.6)% of the time submerged, with a mean dive duration of 25.8 (SE = 0.5) sec. Mean dive duration differed significantly between four periods of the day, as did the mean percent of time spent submerged. During the early morning the animal spent more time at the surface, averaged shorter dives, and was submerged less than other times of day. This is the first study to demonstrate die1 dive cycles in a bottlenose dolphin. Four months after tag loss, the dolphin was photographed with no evidence of necrosis or disfigurement of the dorsal fin. Satellite telemetry was demonstrated as an effective means of documenting the movements and dive behavior of a small inshore cetacean. 相似文献
49.
Isolation of the putative structural gene for the lysine-arginine-cleaving endopeptidase required for processing of yeast prepro-alpha-factor 总被引:85,自引:0,他引:85
S. cerevisiae kex2 mutants are defective for the production of two biologically active secreted peptides: killer toxin and the mating pheromone, alpha-factor. Both molecules are excised from larger precursor polypeptides. In normal cells, the alpha-factor precursor is core-glycosylated and proteolytically processed intracellularly. In kex2 mutants, however, prepro-alpha-factor is not proteolytically cleaved and is secreted in a highly glycosylated form. All kex2 mutants examined (three independent alleles) lack a Zn++-sensitive membrane-associated endopeptidase with specificity for cleaving on the carboxyl side of a pair of basic residues. Absence of this activity cosegregates with the other phenotypes of a kex2 lesion in genetic crosses. The normal KEX2 gene was isolated by complementation of three of the phenotypes conferred by the kex2-1 mutation. The cloned DNA, either on a multicopy plasmid or integrated into the genome, restores both enzymatic activity in vitro and the normal pattern of proteolytic processing and glycosylation of prepro-alpha-factor in vivo. Gene dosage effects suggest that KEX2 is the structural gene for the endopeptidase. 相似文献
50.
Summary
Zymomonas mobilis cells were immobilized into small 1 mm diameter beads of Ca-alginate in order to minimize mass transfer limitations and maximize immobilized cell activity. A combination of small bead size with a high cell concentration of 58 g dry wt. cell per lit. bead volume resulted in high ethanol productivities using a newly designed packed bed bioreactor system. Steady-state dilution rates ranging from 0.4 h-1 to 3.9 h-1 were run resulting in a maximum productivity of 102 g ethanol/l/h for an inlet substrate concentration of 100 g glu/l and 87% conversion. The bioreactor was run continuously at a fixed dilution rate for 384 h and short intermittent treatment of the beads with CaCl2 temporarily increased ethanol productivity to a maximum of 116 g ethanol/l/h. 相似文献