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81.
Transport as the Rate-Limiting Step in the Incorporation of Uridine into Mengovirus Ribonucleic Acid in Novikoff Rat Hepatoma Cells 总被引:3,自引:2,他引:1
The incorporation of uridine into the nucleotide pool of actinomycin-treated, mengovirus-infected Novikoff rat hepatoma cells in culture follows simple Michaelis-Menten kinetics, and the apparent V(max) and K(m) values are similar to those for uridine transport by uninfected cells. Incorporation of uridine into mengovirus-specific ribonucleic acid (RNA) also follows Michaelis-Menten kinetics, and the apparent K(m) (about 10 mum) is approximately the same as for uridine transport. Inhibition of uridine transport by the presence of adenosine, persantin, or phenethyl alcohol inhibits simultaneously and to the same extent the incorporation of uridine into the nucleotide pool and into viral RNA, without affecting viral RNA synthesis per se. Phenethyl alcohol, however, also inhibits virus maturation. The inhibition of uridine incorporation into the nucleotide pool and into viral RNA is of the simple competitive type, indicating that transport into the cells is the rate-limiting step in the incorporation of uridine into mengovirus RNA. The results also indicate that treatment with actinomycin D or mengovirus infection does not affect uridine transport. 相似文献
82.
Linear, Single-Stranded Deoxyribonucleic Acid Isolated from Kilham Rat Virus 总被引:9,自引:9,他引:0
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Kilham rat virus (KRV) was grown in a rat nephroma cell line and was purified by two isopycnic centrifugations in cesium chloride. The virus contains single-stranded deoxyribonucleic acid (DNA) with a molecular weight of approximately 1.6 x 10(6). The DNA was extracted from the virion by both phenol extraction and by 2% sodium dodecyl sulfate at 50 C. KRV DNA, extracted by both procedures, was observed in an electron microscope by using a cytochrome c or diethylaminoethyldextran monolayer. The DNA was also exposed to exonuclease I, an enzyme which hydrolyzes specifically linear, single-stranded DNA. Hydrolysis of 70 to 80% of the DNA was observed. Both the enzymatic and the electron microscope studies support the conclusion that extracted KRV DNA is a single-stranded, linear molecule. The length of the DNA was measured in the electron microscope and determined to be 1.505 +/- 0.206 mum. 相似文献
83.
Derepression of Synthesis of the Aminoacyl-Transfer Ribonucleic Acid Synthetases for the Branched-Chain Amino Acids of Escherichia coli 总被引:5,自引:4,他引:1
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The kinetics of derepression of valyl-, isoleucyl-, and leucyl-transfer ribonucleic acid (tRNA) synthetase formation was examined during valine-, isoleucine-, and leucine-limited growth. When valine was limiting growth, valyl-tRNA synthetase formation was maximally derepressed within 5 min, whereas the rates of synthesis of isoleucyl-, and leucyl-tRNA synthetases were unchanged. Isoleucine-restricted growth caused a maximal derepression of isoleucyl-tRNA synthetase formation in 5 min and derepression of valyl-tRNA synthetase formation in 15 min with no effect on leucyl-tRNA synthetase formation. When leucine was limiting growth, leucyl-tRNA synthetase formation was immediately derepressed, whereas valyl- and isoleucyl-tRNA synthetase formation was unaffected by manipulation of the leucine supply to the cells. These results support our previous findings that valyl-tRNA synthetase formation is subject to multivalent repression control by both isoleucine and valine. In contrast, repression control of iso-leucyl- and leucyl-tRNA synthetase formation is specifically mediated by the supply of the cognate amino acid. 相似文献
84.
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86.
van der Waals Forces between Cylinders: II. Retarded Interaction between Thin Isotropic Rods
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We derive the retarded van der Waals interaction between two long thin parallel dielectric cylinders immersed in a solvent. The result shows that the ultraviolet interactions which may be responsible for the specificity of macromolecular interactions do not operate strongly over distances R ≥ 50 Å. For greater distances the contribution of these frequencies ξ is damped by a factor ∞ e-ξR/c. 相似文献
87.
A mathematical analysis of branched pathway regulation has led to the prediction of a novel homoserine control in Escherichia coli B. Experimental support for such control is presented in this paper. Homoserine, the precursor of both threonine and methionine, inhibits nicotinamide adenine dinucleotide phosphate (NADP(+))-specific glutamate dehydrogenase (EC 1.4.1.4), the enzyme catalyzing the first reaction in ammonia assimilation. Physiological and biochemical evidence for this effect are offered. Homoserine depresses the growth rate of the organism, and glutamate, the product of the inhibited reaction, reverses this effect. The NADP(+)-specific glutamate dehydrogenase activity in cell-free extracts is inhibited by homoserine, and this inhibition parallels the restriction of growth rate. These effects are found in other enteric bacteria which share a similar overall pattern of control for the amino acids derived from aspartate. On the other hand, a sampling of more distantly related species which have different pathways and/or regulatory patterns provides no evidence for homoserine inhibition of the glutamate dehydrogenase reaction. 相似文献
88.
The Fertility of Melanesian Girls, Laboratory Mice, and Prostitutes: A Comment on the "Bruce Effect"
Ann Chowning 《American anthropologist》1969,71(6):1122-1125
Greenfield has recently proposed that low fertility in both prostitutes and unmarried Trobriand girls may be explained by the "Bruce effect": the inhibition of pregnancy in female mice that have had intercourse with different males within a short period. An examination of Malinowski's data indicates that a Trobriand girl usually had intercourse with only one man over a fairly long period and her sex life was not at all comparable to that of a prostitute or one of Bruce's mice. Low fertility in unmarried girls has been well documented for several Melanesian societies that differ notably in the behavior permitted to girls. The existence of so-called adolescent sterility still seems to be the best explanation to cover all of these cases. [fertility, sexual behavior, Melanesia] 相似文献
89.
E. Edward Peeples Ann Geisler Carol J. Whitcraft Clarence P. Oliver 《Biochemical genetics》1969,3(6):563-569
Phenol oxidase activity of activated A1 and A2 (A3) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A1 band and then in the A2 (A3) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05. 相似文献
90.
Method for Assessing the Frequency of Transfer of an R Factor on Solid Media and for Isolating Cells of the Donor Type from a Predominantly Repressed Culture
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A method for assessing the incidence of R factor transfer on solid media is described. The method gives values similar to those obtained with conventional techniques but allows the derepressed cells from a predominantly repressed population to be isolated. 相似文献