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991.
Deoxyribonucleic Acid Polymerase of Rous Sarcoma Virus: Studies on the Mechanism of Double-Stranded Deoxyribonucleic Acid Synthesis 总被引:7,自引:6,他引:1
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Anthony Faras Lois Fanshier Axel-Claude Garapin Warren Levinson J. Michael Bishop 《Journal of virology》1971,7(5):539-548
The deoxyribonucleic acid (DNA) polymerase of Rous sarcoma virus synthesizes both single- and double-stranded DNA, utilizing the ribonucleic acid (RNA) of the viral genome as the initial template. Results of pulse-chase experiments indicate that the single-stranded DNA serves as unconserved template and precursor for the synthesis of double-stranded DNA. The latter reaction is apparently initiated in association with the viral RNA and may involve a partially double-stranded intermediate form. 相似文献
992.
The different types of recrystallization which can be observed in the Triassic involutinids should be considered in the taxonomic treatment of this foraminiferal family. If the diagenetic modifications of the test are neglected the same form could be placed into different suborders. Our inclusion of the genusTriasina Majzon in the Involutinidae proposed earlier on purely morphologic grounds, seems to be supported by the fact that the same types of recrystallization exist inTrocholina, Involutina undTriasina. 相似文献
993.
Summary A model predicting net photosynthesis of individual plant leaves for a variety of environmental conditions has been developed. It is based on an electrical analogue describing gas diffusion from the free atmosphere to the sites of CO2 fixation and a Michaelis-Menten equation describing CO2 fixation. The model is presented in two versions, a simplified form without respiration and a more complex form including respiration. Both versions include terms for light and temperature dependence of CO2 fixation and light control of stomatal resistance. The second version also includes terms for temperature, light, and oxygen dependence of respiration and O2 dependence of CO2 fixation.The model is illustrated with curves based on representative values of the various environmental and biological parameters. These curves relate net photosynthesis to light intensity, [CO2], [O2], temperature, and resistances to CO2 uptake. The shape of the [CO2]-net photosynthesis curves depends on the total diffusion resistance to CO2 uptake and the Michaelis constant for CO2 uptake. The curves range from typical Michaelis-Menten to Blackman types.The model is combined with a model of leaf energy exchange permitting simultaneous estimation of net photosynthesis and transpiration. The combined model is illustrated with curves relating transpiration to photosynthesis under a wide variety of environmental conditions. Environmental regimes yielding maximum efficiency of water use are identified for the given assumptions and biological parameters. 相似文献
994.
Thermus aquaticus contains four major fatty acids, iso-C(15) (28%), iso-C(16) (9%), normal-C(16) (13%), and iso-C(17) (48%), when grown at 70 C, as determined by gas chromatography and mass spectrometry. Small amounts of iso-C(12), normal-C(12:1), iso-C(13), normal-C(14), iso-C(14), and normal-C(15:1) were also detected. A change in growth temperature (50 to 75 C at 5-C intervals) affects a shift in the proportions of some of the fatty acids. The proportions of the monoenoic and branched-C(17) fatty acids decreased and the proportions of the higher-melting iso-C(16) and normal-C(16) fatty acids increased. Cells grown at 75 C contained 70% more total fatty acids than cells grown at 50 C. The largest increases, in absolute amounts, were in the content of iso-C(16) and normal-C(16) fatty acids, with only a 1.6-fold increase in the major iso-C(15) and iso-C(17) fatty acids. There was a 2.5-fold decrease in normal-C(15:1) and at least a 24-fold decrease in anteiso-C(17), which is present at 50 and 55 C but not at higher temperatures. There was no difference in proportion or amount of fatty acids between exponential and stationary-phase cells grown at 70 C. When cells were grown on glutamate instead of yeast-extract and tryptone at 70 C, the total fatty acid content remained constant, but there was an increase in the proportions of iso-C(16) and normal-C(16) fatty acids concomitant with a decrease in the proportions of the iso-C(15) and iso-C(17) fatty acids. 相似文献
995.
Michael Sinensky 《Journal of bacteriology》1971,106(2):449-455
The higher the growth temperature of Escherichia coli cultures the greater is the proportion of saturated fatty acids in the bacterial phospholipids. When fatty acids are exogenously supplied to E. coli, higher growth temperatures will likewise increase the relative incorporation of saturated fatty acids into phospholipids. One of the steps in the utilization of fatty acids for phospholipid biosynthesis is, therefore, temperature-controlled. The temperature effect observed in vivo with mixtures of 3H-oleate and 14C-palmitate is demonstrable in vitro by using mixtures of the coenzyme A derivative of these fatty acids for the acylation of α-glycerol phosphate to lysophosphatidic and phosphatidic acids. In E. coli extracts, the relative rates of transacylation of palmityl and oleyl coenzyme A vary as a function of incubation temperature in a manner which mimics the temperature control observed in vivo. The phosphatidic acid synthesized in vitro shows a striking enrichment of oleate at the β position analogous to the positional specificity observed in phospholipids synthesized in vivo. 相似文献
996.
Antiserum was made against a single 30S protein, 30S-7. The amount of complement fixed by total 30S protein in the presence of this antiserum indicated that protein 30S-7 was the major antigen in the mixture of proteins. Each of the 30S ribosomal proteins was tested for cross-reactivity with anti-30S-7. This was done by determining if any of the other 30S proteins inhibited complement fixation by 30S-7. None of the other 30S proteins was found to inhibit complement fixation by 30S-7, indicating that 30S-7 is antigenically distinct from the other proteins. 相似文献
997.
Howard Feit Gary R. Dutton Samuel H. Barondes Michael L. Shelanski 《The Journal of cell biology》1971,51(1):138-147
The subunit protein of microtubules, tubulin, has been demonstrated to be present in isolated nerve endings by gel electrophoresis, amino acid composition, and peptide mapping. The tubulin constitutes approximately 28% of the soluble protein of the nerve endings. The transport of tubulin to the nerve endings has been demonstrated and its relationship to slow transport is discussed. 相似文献
998.
Summary Nitrogen fixation in the natural, Agropyron-Koeleria grassland ecosystem was studied using the C2H2-C2H4 and N15 assays. Small soil samples and also undisturbed soil cores were used for analyses. Both techniques indicated that grassland
and associated cultivated soils had low fixation rates (0.6–1.8 kg/ha per 28 days in the laboratory and, 1 kg/ha per season
under actual field conditions). Algal colonies (Nostoc spp.) on the soil surface were active fixers when the surface of the grassland was moist. However, their small biomass limits
the extent of fixation in most areas.
In native grassland, 16 legumes bore nodules. The three most common speciesVicia americana, Thermopsis rhombifolia andOxytropis sericea, all of which had active nodules, contributed 10 per cent of the total nitrogenase activity.
The non-legumesElaeagnus commutata andShepherdia argentea were profusely nodulated with active nodules, but were confined to specific habitats. No nodules were found onArtemisia orOpuntia spp.
The major, heterotrophic, asymbiotic bacteria in the soil were clostridia. These utilize substrates produced by aerobic cellulose
and hemicellulose degrading organisms to fix N in anaerobic microsites. The C2H2:N2 reduction ratio was 3 to 1 in large, aerobic core samples, but was greater under water-logged conditions where high fixation
rates occurred. 相似文献
999.
Current psychological research into the inference (diagnostic) process is briefly reviewed, using as a vehicle an investigation
of the prediction of the probability of success of hypothetical applicants to a graduate program in biology. Brunswik’s lens
model and multiple regression analysis are used, as is a Bayesian approach. Four judges’ (biologists’) predictions are analyzed.
Some general conclusions about inference, drawn from the current data in psychology, are presented.
This investigation was supported by PHS Research Grant No. MH-17487-01 from the National Institute of Mental Health. 相似文献
1000.
A large proportion of cannery workers see a doctor only as a last resort, in time of crisis. The Cannery Workers Multiphasic Screening Program identified workers in need of physician evaluation, and referred each to a physician of his choice, for examination by appointment, while the worker was not acutely ill. In many instances the screening program generated the first encounters between patient and physician. It conducted a follow-up system for workers unaccustomed to methodical health care. The program financed pretesting education of the persons to be tested, multiphasic testing, physician evaluation of abnormal findings, and the follow-up reminder system.Each physician, in advance of the appointment for evaluation, was sent a computerized report calling attention to findings that exceeded limits considered normal. The report included a form facilitating the physician''s report and billing. In counties having foundations for medical care, the foundations reviewed the form for adequacy of follow-up and appropriateness of charges.The effort to bridge the gap between findings, diagnosis and therapy, for a population group newly introduced to modern medical care delivery, was made possible by the use of the computer as a tool for the attainment of specific, preanalyzed components of the total objective. 相似文献