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31.
The available amino acid sequences of the α-amylase family (glycosyl hydrolase family 13) were searched to identify their
domain B, a distinct domain that protrudes from the regular catalytic (β/α)8-barrel between the strand β3 and the helix α3. The isolated domain B sequences were inspected visually and also analyzed
by Hydrophobic Cluster Analysis (HCA) to find common features. Sequence analyses and inspection of the few available three-dimensional
structures suggest that the secondary structure of domain B varies with the enzyme specificity. Domain B in these different
forms, however, may still have evolved from a common ancestor. The largest number of different specificities was found in
the group with structural similarity to domain B from Bacillus cereus oligo-1,6-glucosidase that contains an α-helix succeeded by a three-stranded antiparallel β-sheet. These enzymes are α-glucosidase,
cyclomaltodextrinase, dextran glucosidase, trehalose-6-phosphate hydrolase, neopullulanase, and a few α-amylases. Domain B
of this type was observed also in some mammalian proteins involved in the transport of amino acids. These proteins show remarkable
similarity with (β/α)8-barrel elements throughout the entire sequence of enzymes from the oligo-1,6-glucosidase group. The transport proteins, in
turn, resemble the animal 4F2 heavy-chain cell surface antigens, for which the sequences either lack domain B or contain only
parts thereof. The similarities are compiled to indicate a possible route of domain evolution in the α-amylase family.
Received: 4 December 1996 / Accepted: 13 March 1997 相似文献
32.
N. J. H. CAMPBELL F. C. HARRISS M. S. ELPHINSTONE P. R. BAVERSTOCK 《Molecular ecology》1995,4(4):407-418
The ability of DNA screening techniques such as Temperature Gradient Gel Electrophoresis (TGGE) and Heteroduplex Analysis to provide resolution approaching that provided by DNA sequencing for a fraction of the time, effort and expense point to them as the logical successor to allozyme electrophoresis for population genetics. Here we present a novel alternative to the standard TGGE/Heteroduplex Analysis protocol - Outgroup Heteroduplex Analysis (OHA). We assess this technique's sensitivity in comparison to previous screening approaches using a known hierarchy of sequence differences. Our data show that Outgroup Heteroduplex Analysis has greatly increased sensitivity for screening DNA variants from that of TGGE used alone and is easily applicable to large numbers of samples. Using this technique we can consistently detect differences of as small as one base change in a 433-base-pair fragment of Control Region mitochondrial DNA from Melomys cerbinipes (an Australian rodent). The approach should easily be extendable to nuclear loci and is not necessarily dependent on the use of a denaturing gradient When combined with a targeted sequencing effort, OHA provides a sensitive and simple means of obtaining allele/haplotype frequencies and their phylogenies for population and phylogeographic studies in molecular ecology. 相似文献
33.
34.
Summary Microbial degradation of the leaf litter ofShorea robusta Gaertn. was studied for a period of one year. The changes in the major litter constituents like sugar, starch, hemicellulose,
cellulose and lignin were analysed from the litter kept under the nylon bags, at a month's interval. Four major elements phosphorous,
potassium, magnesium and calcium were also assessed monthly from the decaying litter and the soil. The role of microfungi
in mineral cycling and loss of litter substrates have been correlated. 相似文献
35.
B. Thompson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1978,52(5):201-207
Summary Examples are presented to illustrate some of the effects aberrant values, in particular, measurement errors, may have on estimates of the genetic parameters related to selection studies. It is shown that aberrant values may cause observed response to selection pressure to differ considerably from predicted response. Possible dangers of indiscriminate screening are also discussed. 相似文献
36.
J. K. Bull K. E. Basford I. H. DeLacy M. Cooper 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,85(4):461-469
Summary Several subjective choices must be made when classifying genotypes based on data from plant breeding trials. One choice involves the method used to weight the contribution each environment makes to the classification. A second involves the use of either genotype-means for each environment or genotypevalues for each block, i.e., considering each block to be a different environment. Another involves whether environments (or blocks) in which genotypes are nonsignificantly different should be included or excluded from such classifications. An alternative to the use of raw or standardized data, is proposed in which each environment is weighted by a discrimination index (DI) that is based on the concept of repeatability. In this study the effect of three weighting methods (raw, standardized and DI), the choice of using environments or blocks, and the choice of including or excluding environments or blocks in which genotypic effects were not significant, were considered in factorial combination to give 12 options. A data set comprised of five check cultivars each repeated six times in each of three blocks at six environments was used. The effect of these options on the ability of a hierarchical clustering technique to correctly classify the repeats into five groups, each consisting of all the six repeats of a particular check cultivar, was investigated. It was found that the DI weighting method generally led to better recovery of the known structure. Using block data rather than environmental data also improved structure recovery for each of the three weighting methods. The exclusive use of environments in which genotypic effects were significant decreased structure recovery while the contrary generally occurred for blocks. The best structure recovery was obtained from the DI weighting applied to blocks (whether genotypes were significant or not). 相似文献
37.
Chronobiologic Evaluation of Drug Efficacy in Hypertension 总被引:1,自引:0,他引:1
Kohji Tamura 《Chronobiology international》1991,8(6):511-525
Time-associated variations of blood pressure became accesible due to the modern development of pressure monitoring technology. The data collection and analysis should be standardized and formulated. Time-associated changes of pressure were evaluated not only by nonparametric and conventional but also by parametric and rhythmometric estimation. The reference data (chronodesms) are essential to define the deviant magnitude of pressure. This chronobiologic approach became feasible to quantitate the efficacy of antihypertensive agents in hypertensives. 相似文献
38.
Abstract. Woody vegetation was studied in 44 sites in Senegal. Species composition and density were analysed with TWINSPAN and Canonical Correspondence Analysis; 16 vegetation types were defined. A supervised, multispectral and multitemporal classification of day and night, dry season NOAA-AVHRR imagery was used to identify their distribution with a classification accuracy ranging from 60–100%. 相似文献
39.
L. Kálmán M. Dévényi 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1982,62(3):209-212
Summary Simple correlations were calculated between nine different cms sources (cms-S, -R, -ML, -L, -CA, -EK, -C, -Rb, -T) on the basis of the weighted restoring reactions of 41 inbred lines. The Principal Component Analysis was applied to a 9 × 9 matrix which clearly grouped cytoplasms according to their similarities. The Principal Component I included S, R, ML, L, CA and EK cytoplasms; the Principal Component II contained C and Rb cytoplasms while T-cytoplasms was placed in Principal Component III. This corresponds to the main groupings indicated in the literature (Beckett 1971). However, after varimax rotation of the Principal Components, the S main group, including the 6 tested cytoplasms, fell into 3 subgroups: I.: S, R, ML; II.: L, CA; III.: EK.These data indicate that the Principal Component Analysis can be used to select a limited number of cms sources from the S group, representing the variability of the cytoplasmic gene pool of that group. 相似文献
40.
Bruno David 《Geobios》1980,13(6):903-926
A complete study of the ontogeny of the irregular urchin Toxaster granosus kiliani (Lambert)) was achieved from an important lower cretaceous sample. In a first time, ontogenic variations of each character were analysed versus length chosen as size reference. This first step had shown that very important changes in shape take place during the development of the young urchin: increase in height, downward migration of the periproct, forward movement of the peristome… In a second time, a growth crisis was proved and described. Such a crisis occurs, from 12 mm to 16 mm length, as a momentary acceleration of the growth (i.e. the rate of growth increases during a short time). The reality of this crisis was demonstrated by both mathematical and biological ways and also by comparing with other actual and fossil populations. The whole of these results leads to a synthetical pattern of growth divided into three main stages which are successively a juvenile, a preadult and an adult stage. This division was proved also by a principal components analysis. 相似文献