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71.
The sequence organization of four different families of Y chromosomal repetitive DNA is characterized at three levels of spatial extension along the Y chromosome of Drosophila hydei. At the lowest level of resolution, DNA blot analysis of Y chromosomal fragments of different lengths and in situ hybridization experiments on metaphase chromosomes demonstrate the clustering of each particular sequence family within one defined region of the chromosome. At a higher level of resolution, family specific repeats can be detected within these clusters by crosshybridization within 10–20 kb long continuous stretches of cloned DNA in EMBL3 phages. At the highest level of resolution, detailed sequence analysis of representative subclones about 1 kb in length reveals a satellite-like head to tail arrangement of family specific degenerated subrepeats as the building scheme common to all four families. Our results provide the first comparative sequence analysis of three novel families of repetitive DNA on the long arm of the F chromosome of D. hydei. Additional data are presented which support the existence of two related subfamilies of repetitive DNA on the short arm of the Y chromosome. 相似文献
72.
Carbohydrate side chains of Rauscher leukemia virus envelope glycoproteins are not required to elicit a neutralizing antibody response. 总被引:8,自引:4,他引:4 下载免费PDF全文
Antisera raised against Rauscher leukemia virus (R-MuLV) contain a preponderance of antibodies against glycoprotein gp70 that are dependent on the presence of carbohydrate side chains for reactivity, as judged by immunoprecipitation or Western blotting. However, the majority of neutralizing antibodies were not dependent on the presence of carbohydrate, as indicated by (i) the ability of deglycosylated R-MuLV to adsorb neutralizing antibody from sera as efficiently as glycosylated R-MuLV and (ii) the ability of deglycosylated R-MuLV to induce neutralizing antibody responses when injected into rabbits. Moreover, a faster response was obtained with deglycosylated R-MuLV than with untreated control virus in the latter experiments. The results indicate that the neutralizing antibodies are a discrete subpopulation of the total antibody response. Furthermore, the carbohydrate moieties appear to afford protection to the virion during infection, rather than serve as a target for neutralization. 相似文献
73.
The regulation of''early'' enzymes during the development and dedifferentiation of Dictyostelium discoideum 总被引:2,自引:0,他引:2
Stephen Alexander Ann Mane Cibulsky Lee Mitchell David R. Soll 《Differentiation; research in biological diversity》1985,30(1):1-6
The specific activities of the enzymes alpha-mannosidase and N-acetylglucosaminidase increase immediately after the initiation of the development of bacterially grown cell cultures of Dictyostelium discoideum. The regulation of these two enzymes was found to be dissociable in the developmental timer mutant, FM-1, which aggregates 4.5 h earlier than wild-type cells due to the absence of the first rate-limiting component of the preaggregative period. The increase in alpha-mannosidase activity occurs in the absence of the first rate-limiting component, but the increase in N-acetylglucosaminidase activity does not. These results indicate the following: (1) the increase in the specific activity of alpha-mannosidase is not related to the timing of subsequent developmental stages; (2) the increase in the specific activity of N-acetylglucosaminidase is not necessary for the subsequent developmental program; and (3) either the increase in the specific activity of N-acetylglucosaminidase is dependent upon progress through the first rate-limiting component, or the increase in this enzyme activity and the first rate-limiting component are both dependent upon an early event for which FM-1 is defective. In addition to early development, we monitored the two enzyme activities during dedifferentiation. The results demonstrate that there is no difference between dedifferentiating wild-type cells and dedifferentiation-defective mutant HI-4 cells. Changes in enzyme specific activity accompanying dedifferentiation are dependent upon the composition of the dedifferentiation-inducing media and are consistent with the levels of these enzymes observed in cells growing in the different nutrient media. 相似文献
74.
l-Amino acid oxidase is synthesized in Neurospora crassa in response to three different physiological stimuli: (i) starvation in phosphate buffer, (ii) mating, and (iii) nitrogen derepression in the presence of amino acids. During starvation in phosphate buffer, or after mating, l-amino acid oxidase synthesis occurred in parallel with that of tyrosinase. Exogenous sulfate repressed the formation of the two enzymes in starved cultures, but not in mated cultures. Sulfate repression was relieved by protein synthesis inhibitors, suggesting that the effect of sulfate required the synthesis of a metabolically unstable protein repressor. With amino acids as the sole nitrogen source only l-amino acid oxidase was produced. Under these conditions enzyme synthesis was repressed by ammonium and was insensitive to sulfate. Biochemical evidence suggested that the l-amino acid oxidase formed under the three different conditions was the same protein. Therefore, the expression of l-amino acid oxidase appeared to be under the control of least two regulatory circuits. One, also controlling tyrosinase, seems to respond to developmental signals related to sexual morphogenesis. The other, controlling other enzymes of the nitrogen catabolic system, is used by the organism to obtain nitrogen from alternative sources such as proteins and amino acids. 相似文献
75.
Effects of dissolved organic carbon and second substrates on the biodegradation of organic compounds at low concentrations 总被引:9,自引:0,他引:9
Pseudomonas acidovorans and Pseudomonas sp. strain ANL but not Salmonella typhimurium grew in an inorganic salts solution. The growth of P. acidovorans in this solution was not enhanced by the addition of 2.0 micrograms of phenol per liter, but the phenol was mineralized. Mineralization of 2.0 micrograms of phenol per liter by P. acidovorans was delayed 16 h by 70 micrograms of acetate per liter, and the delay was lengthened by increasing acetate concentrations, whereas phenol and acetate were utilized simultaneously at concentrations of 2.0 and 13 micrograms/liter, respectively. Growth of Pseudomonas sp. in the inorganic salts solution was not affected by the addition of 3.0 micrograms each of glucose and aniline per liter, nor was mineralization of the two compounds detected during the initial period of growth. However, mineralization of both substrates by this organism occurred simultaneously during the latter phases of growth and after growth had ended at the expense of the uncharacterized dissolved organic compounds in the salts solution. In contrast, when Pseudomonas sp. was grown in the salts solution supplemented with 300 micrograms each of glucose and aniline, the sugar was mineralized first, and aniline was mineralized only after much of the glucose carbon was converted to CO2. S. typhimurium failed to multiply in the salts solution with 1.0 micrograms of glucose per liter. It grew slightly but mineralized little of the sugar at 5.0 micrograms/liter, but its population density rose at 10 micrograms of glucose per liter or higher. The hexose could be mineralized at 0.5 micrograms/liter, however, if the solution contained 5.0 mg of arabinose per liter.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
76.
Minimum bacterial density for bacteriophage replication: implications for significance of bacteriophages in natural ecosystems 总被引:11,自引:0,他引:11
Bacteriophage 80 alpha did not increase in number in cultures containing less than about 1.0 X 10(4) to 1.5 X 10(4) CFU of Staphylococcus aureus per ml, but bacteriophage replication did occur when the number of bacteria exceeded this density, either initially or as a result of host cell multiplication. The minimum density of an asporogenous strain of Bacillus subtilis required for an increase in the number of bacteriophage SP beta cI was about 3 X 10(4) CFU/ml. The threshold density of Escherichia coli for the multiplication of bacteriophage T4 was about 7 X 10(3) CFU/ml. In the presence of montmorillonite, bacteriophage T4 did not increase in number until the E. coli population exceeded 10(4) CFU/ml. The mineralization of glucose was not affected in E. coli cultures inoculated with a low number of bacteriophage T4, but it could not be detected in cultures inoculated with a large number of phage. The numbers of bacteriophage T4 and a bacteriophage that lyses Pseudomonas putida declined rapidly after being added to lake water or sewage. We suggest that bacteriophages do not affect the number or activity of bacteria in environments where the density of the host species is below the host cell threshold of about 10(4) CFU/ml. 相似文献
77.
The kinetics of mineralization of a wide range of concentrations of benzoate, glucose, and benzylamine by Pseudomonas sp., Salmonella typhimurium, and microorganisms in acclimated sewage was studied. The treatment of initial substrate concentration and population density as independent variables in nonlinear regression analysis permitted the estimation of a single value for each of the parameters of Monod kinetics that best described the mineralization of substrate at each concentration by the pure cultures and the sewage microflora. One value for each of the parameters of Monod kinetics was used for each of the three compounds to produce theoretical curves which lay close to the observed data on mineralization. Statistically significant differences existed in the values of the parameters of Monod kinetics that best described mineralization in cultures differing only in initial substrate concentration and cell density. However, for the compounds tested, the variance left by analyses using one value for each parameter of Monod kinetics was less than double the unexplained variance left by individual analyses of the data from each treatment. Although significant, this increase is small compared with the amount of variance that could be explained using only one value for each parameter of Monod kinetics. 相似文献
78.
An observation of episodic feeding and growth of larval Leiostomus xanthurus in the northern Gulf of Mexico 总被引:1,自引:0,他引:1
Govoni John J.; Chester Alexander J.; Hoss Donald E.; Ortner Peter B. 《Journal of plankton research》1985,7(1):137-146
Four cruises were conducted in the northern Gulf of Mexico overtwo spawning seasons of the sciaenid fish Leiostomus xanthurus.On only one occasion did unusually high densities of larvaeand their principal microzooplanktonic foods co-occur. Peakdensities of larvae and microzooplankton were observed in athin lens of cool surface water that characterized a hydrographicdiscontinuity, and all larvae contained high numbers of foodorganisms in their guts. Instantaneous exponential growth ratesestimated from measurements of otolith growth increments, indicatedaccelerated growth on the day that larvae were collected. Alaboratory experiment verified that larval L. xanthurus respondsto an increased ration with accelerated growth that is detectableon otoliths. Together these data suggest that the spatial distributionof L. xanthurus larvae and their microzooplanktonic food ispatchy and that interactions of larvae and microzooplanktonmay be episodic. 相似文献
79.
The elastic properties of the hind feet of Donkeys, and of tendons removed from the feet, have been investigated by methods similar to those used in a previous study of the forefoot. The elastic strain energy stored in the foot, during a trotting step, is calculated to be approximately the optimum which would minimize the work required of the muscles in this gait. 相似文献
80.
R M Alexander 《Journal of theoretical biology》1984,109(4):621-636
Limb bones are liable to fail by fatigue, due to stresses imposed repeatedly in activities such as running. They may also be broken by larger stresses which occur occasionally in accidents. Too weak a bone will probably fail but too strong a bone is unduly heavy. A mathematical model predicts optimum strengths for bones subject to the hazards both of fatigue and of accidents. When accidents are mild and predictable, fatigue is the more important hazard. When they are large and unpredictable they are the more important hazard and stronger bones are generally preferred, but in extreme cases it may become advantageous to dispense with the bone. There is a restricted range of circumstances in which fatigue and accidents are both important hazards. The strengths of many limb bones seem surprisingly low, in the light of the theory and of current knowledge of the fatigue properties of bone. 相似文献