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51.
Evolution and Extinction of Transposable Elements in Mendelian Populations 总被引:8,自引:2,他引:6 下载免费PDF全文
A model of the evolution of a transposable element family in a Mendelian host population is proposed that incorporates heritable phenotypic mutations in the elements. The temporal behavior of the numbers of mutant and wild-type elements is studied, and the expected extinction time of the transposable element family is examined. Our results indicate that, if the mutant can be transposed equally well in the presence of the wild type, then it can be expected to be found in preponderance, whereas elements, such as retroviruses, where the transposing genome and its phenotypic expression are coupled, may be characterized by a low mutant frequency. 相似文献
52.
T. Norman Palmer Margaret A. Caldecourt Keith Snell Mary C. Sugden 《Bioscience reports》1985,5(12):1015-1033
Branched-chain amino acid metabolism in skeletal muscte promotes the production of alanine, an important precursor in hepatic gluconeogenesis. There is controversy concerning the origin of the carbon skeleton of alanine produced in muscle, specifically whether it is derived from carbohydrate via glycolysis (the glucose-alanine cycle) or from amino acid precursors (viz. glutamate, valine, isoleucine, methionine, aspartate, asparagine) via a pathway involving phosphoenolpyruvate (PEP) carboxykinase and pyruvate kinase, or NADP-malate dehydrogenase (malic enzyme). The relevant literature is reviewed and it is concluded that neogenic flux from amino acids is unlikely to be of major quantitative importance for provision of the carbon skeleton of alanine either in vitro or in vivo. Evidence is presented that branched-chain amino acid oxidation in muscle is incomplete and that the branched-chain 2-oxo acids and the products of their partial oxidation (including glutamine) are released. The role of these metabolites is discussed in the context of fuel homeostasis in starvation. 相似文献
53.
Transposon-like properties of the major, long repetitive sequence family in the genome of Physarum polycephalum 总被引:3,自引:1,他引:2 下载免费PDF全文
A family of long, highly-repetitive sequences, referred to previously as `HpaII-repeats', dominates the genome of the eukaryotic slime mould Physarum polycephalum. These sequences are found exclusively in scrambled clusters. They account for about one-half of the total complement of repetitive DNA in Physarum, and represent the major sequence component found in hypermethylated, 20-50 kb segments of Physarum genomic DNA that fail to be cleaved using the restriction endonuclease HpaII. The structure of this abundant repetitive element was investigated by analysing cloned segments derived from the hypermethylated genomic DNA compartment. We show that the `HpaII-repeat' forms part of a larger repetitive DNA structure, ~8.6 kb in length, with several structural features in common with recognised eukaryotic transposable genetic elements. Scrambled clusters of the sequence probably arise as a result of transposition-like events, during which the element preferentially recombines in either orientation with target sites located in other copies of the same repeated sequence. The target sites for transposition/recombination are not related in sequence but in all cases studied they are potentially capable of promoting the formation of small `cruciforms' or `Z-DNA' structures which might be recognised during the recombination process. 相似文献
54.
Abstract Hydrogen fluoride treatment of [14 C-glycerol]lipoteichoic acid synthesized by growing Streptococcus faecium ATCC9790 in the presence of 1,3[14 C]glycerol produced five radioactive, water-soluble products which were identified by chromatographic and analytical techniques to be tetraglucosyl glycerol, triglucosyl glycerol, diglucosyl glycerol, monoglucosyl glycerol and unsubstituted glycerol. The percent composition of each varied modestly from culture to culture and ranged between 7 and 8% for the tetra-, 20.5 and 31.2% for the tri-, 11.3 to 23.5% for the di-, 20.9 to 26.8% for the mono-, and 23.1 to 34.8% for the unsubstituted glycerol. The same glucosylated glycerol compounds could be obtained in an in vitro reaction in which a 30 000 × g particulate enzyme catalyzed the incorporation of [3 H]glucose from UDP [3 H]glucose into lipoteichoic acid. 相似文献
55.
Noni E. MacDonald Susan Collison Norman Wolfish Peter N. McLaine Andrew M. Mackenzie 《CMAJ》1985,133(12):1211-1213
To determine the effectiveness of precleansing with chlorhexidine gluconate-cetrimide in reducing the contamination rate of bagged urine specimens, 62 infants admitted to a children''s hospital were randomly assigned to either receive (32 infants) or not receive (30) cleansing before bag application. Perimeatal swabs were taken before bag application and, in the treated group, after cleansing. Of the specimens from the treated group 69% were found to be contaminated, compared with 73% of those from the no-cleansing group. Chlorhexidine was ineffective in eliminating the perimeatal flora in 75% of the infants. The same organisms were present on the perimeatal swab and in the urine specimen in 95% of the infants in the treated group and 96% of those in the no-cleansing group. To estimate the contamination rate of urine specimens routinely cultured in the laboratory, 200 consecutive specimens (142 midstream and 58 bagged) were cultured. The contamination rate of the midstream urine specimens was 15%, compared with 66% for the bagged speciments. The cost of laboratory processing of contaminated bagged urine specimens at the hospital in 1983 may have been as high as $13 365. Chlorhexidine cleansing does not appear to be cost-effective. Further randomized controlled studies are needed to evaluate the effectiveness of other cleansing agents in reducing the contamination rate of bagged urine specimens. 相似文献
56.
Patsy M. Brannon Bonnie M. Orrison Norman Kretchmer 《In vitro cellular & developmental biology. Plant》1985,21(1):6-14
Summary Rat pancreatic acinar cells were isolated and cultured in Ham's F12 medium with 15% bovine calf serum. Caerulein, insulin,
somatostatin, and dexamethasone (DEX) had no effect on intracellular or secreted amylase in these cultured cells. A serum-free
medium, using Waymouth's MB 752/1 supplemented with albumin, epidermal growth factor (EGF), DEX, and HEPES, was then developed
to avoid serum factors that might mask hormonal effects. In this SF medium, pancreatic acinar, cells maintained the morphological
and ultrastructural characteristics of freshly isolated cells and secreted amylase in response to the secretagogue, carbamyl
choline. Insulin, at a concentration of 1 μg/ml, significantly increased intracellular and secreted amylase activity after
3 d. This model cell system can be used to study the regulation of the synthesis of amylase and other pancreatic enzymes in
vitro. 相似文献
57.
Three new in vivo metabolites of 1 alpha,25-dihydroxyvitamin D3 were isolated from the serum of dogs given large doses (two doses of 1.5 mg/dog) of 1 alpha,25-dihydroxyvitamin D3. The metabolites were isolated and purified by methanol-chloroform extraction and a series of chromatographic procedures. By cochromatography on a high-performance liquid chromatograph, ultraviolet absorption spectrophotometry, mass spectrometry, Fourier-transform infrared spectrophotometry, and specific chemical reactions, the metabolites were identified as 1 alpha,25-dihydroxy-24- oxovitamin D3, 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, and 1 alpha,24(S),25-trihydroxyvitamin D3. According to these procedures, the total amounts of the isolated metabolites were as follows: 1 alpha,25-dihydroxyvitamin D3, 23.6 micrograms; 1 alpha,25-dihydroxy-24- oxovitamin D3, 1.8 micrograms; 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, 9.2 micrograms; 1 alpha,24(R),25-trihydroxyvitamin D3, 15.4 micrograms; 1 alpha,24(S),25-trihydroxyvitamin D3, 1.0 microgram. With recovery corrections, the serum levels of each metabolite were approximately 49 ng/mL for 1 alpha,25-dihydroxyvitamin D3, 3.7 ng/mL for 1 alpha,25-dihydroxy-24- oxovitamin D3, 19 ng/mL for 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, 32 ng/mL for 1 alpha,24(R),25-trihydroxyvitamin D3, and 2.1 ng/mL for 1 alpha,24(S),25-trihydroxyvitamin D3. 相似文献
58.
Murine monoclonal antibodies to membrane antigens were generated by immunization with a crude cellular membrane preparation from suspension-cultured cells of Nicotiana glutinosa L. From a panel of thirteen monoclonal antibodies, seven were found to be directed against antigens present on the plasma-membrane by immunofluorescence visualization of antibody binding to the surface of isolated protoplasts. The corresponding set of plasma-membrane antigen(s) were present in root, shoot and leaf tissue and some but not all of these antigens were of wide species distribution, being found in Nicotiana tabacum L., N. plumbaginifolia L., Glycine max L., Phaseolus vulgaris L. and Triticum aestivum L. Topologically specific labeling of intact protoplasts with a monoclonal antibody reactive with an epitope present on the plasma-membrane specifically labeled a membrane fraction which equilibrated at a density of 1.14 kg/l following centrifugation in a sucrose gradient. In addition to use as biochemical markers for fractionation and molecular characterization of plasma-membranes, these monoclonal antibodies provide the basis for new selection tools in plant cell and gene manipulations. 相似文献
59.
The chlorophyll-protein and polypeptide composition of manganese deficient and control sugar beet thylakoids was examined using three different detergent-electrophoresis systems. On a per chlorophyll basis, manganese deficiency reduced the amounts of CPa complex (separated by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis), and CP 47 and CP 43 complexes (separated by octylglucoside/SDS-polyacrylamide gel electrophoresis) without decreasing the amounts of light harvesting complexes. Lithium dodecylsulfate/Triton X-100 polyacrylamide gel electrophoresis showed that manganese deficiency decreased several thylakoid polypeptides, including a chlorophyll b containing 30 kilodalton chlorophyll-protein complex, but did not decrease the amounts of 28 and 29 kilodalton light-harvesting chlorophyll b-containing polypeptides. 相似文献
60.
Photosynthetic electron transport capacity was varied in vivo in sugar beets using iron deficiency, and its effects on the light modulation of ribulose bisphosphate carboxylase (RuBPCase) studied. Three treatment groups corresponding to decreasing amounts of thylakoids per leaf area were examined: iron sufficient (control), moderately iron-stressed, and severely iron-stressed. Reduction in electron transport capacity in vivo was correlated with a substantial decrease in the level of RuBPCase activation, even at saturating irradiances. These results indicate a direct relationship between RuBPCase activation and photosynthetic electron transport. In addition, our data suggest that the activation of RuBPCase could not solely account for the increases in the photosynthetic rate at high irradiances; RuBPCase reached maximal activation at irradiances well below light saturation for net photosynthesis.Abbreviations Chl
chlorophyll
- FeCN
ferricyanide
- FBPase
fructose 1,6-bisphosphatase
- RuBP
ribulose 1,5-bisphosphate
- RuBPCase
ribulose 1,5-bisphosphate carboxylase
- SBPase
sedoheptulose 1,7-bisphosphatase 相似文献