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11.
Jaromir Konecny Michael Eckert Michael Schöniger G. Ludwig Hofacker 《Journal of molecular evolution》1993,36(5):407-416
Summary We lay new foundations to the hypothesis that the genetic code is adapted to evolutionary retention of information in the
antisense strands of natural DNA/RNA sequences. In particular, we show that the genetic code exhibits, beyond the neutral
replacement patterns of amino acid substitutions, optimal properties by favoring simultaneous evolution of proteins encoded
in DNA/RNA sense-antisense strands. This is borne out in the sense-antisense transformations of the codons of every amino
acid which target amino acids physicochemically similar to each other. Moreover, silent mutations in the sense strand generate
conservative ones in its antisense counterpart and vice versa. Coevolution of proteins coded by complementary strands is shown
to be a definite possibility, a result which does not depend on any physical interaction between the coevolving proteins.
Likewise, the degree to which the present genetic code is dedicated to evolutionary sense-antisense tolerance is demonstrated
by comparison with many randomized codes. Double-strand coding is quantified from an information-theoretical point of view. 相似文献
12.
The aim of this study was to delineate the flow patterns in a non-unidirectional flow field inside a ventricle-shaped cell
culture chamber, and examine the resulting morphology and integrity of the endothelium in select regions of the monolayer.
The chamber was perfused by pulsatile flow, and the coherent motion of the fluid was studied using flow visualization aided
by image analysis. Four distinct flow patterns were discerned and examined: central jet, flow impingement, flow separation,
and recirculating eddies. The influence of these patterns on endothelial cell morphology was assessed after 20 h of exposure
to flow. There were no signs of damage to the endothelium in the jet region nor was there evidence of cell alignment with
the flow. Yet, there were changes in cell morphology and cytoskeletal architecture as compared to control. By contrast, within
the eddies where the flow was highly disturbed, there was apparent damage to the endothelium. Thus, exposure of cells to random
velocity fluctuations in regions of quasi-static flow compromises the integrity of the monolayer. Identification of such sites
and acquisition of the knowledge necessary to protect the cells from denudation will be valuable for the endothelialization
efforts of cardiac prostheses. 相似文献
13.
14.
The high-affinity uptake system of phosphatelimited cyanobacterium Anacystis nidulans [Synechococcus leopoliensis (Raciborski) Komarek] is characterized by a threshold value below which uptake cannot occur. Here it is shown that, if phosphate-limited cyanobacteria are challenged with a short pulse of high phosphate concentration that appreciably exceeds this threshold value, the uptake system undergoes an adaptive response, leading to the attainment of new kinetic properties and a new threshold value. These new properties are maintained for several hours after the pulse. A notable characteristic of this new state is a wide linear dependence of the uptake rate on the external phosphate potential that is a function of the driving force of the uptake process. According to theoretical arguments it is shown that this “linear operation mode” can be explained by the simultaneous operation of several uptake systems with different, staggered threshold values and kinetic properties. Moreover, the new linear uptake properties, in turn, reflect the prehistory of phosphate supply experienced by the population. The consequences of this result with regard to environmental fluctuations of the phosphate concentration in lakes are discussed. 相似文献
15.
A method for determining the position and size of optimal sequence regions for phylogenetic analysis
M. J. Martin F. González-Candelas F. Sobrino J. Dopazo 《Journal of molecular evolution》1995,41(6):1128-1138
The availability of fast and accurate sequencing procedures along with the use of PCR has led to a proliferation of studies of variability at the molecular level in populations. Nevertheless, it is often impractical to examine long genomic stretches and a large number of individuals at the same time. In order to optimize this kind of study, we suggest a heuristic procedure for detection of the shortest region whose informational content can be considered sufficient for significant phylogenetic reconstruction. The method is based on the comparison of the pairwise genetic distances obtained from a set of sequences of reference to those obtained for different windows of variable size and position by means of a simple index. We also present an approach for testing whether the informative content in the stretches selected in this way is significantly different from the corresponding content shown by the larger genomic regions used as reference. Application of this test to the analysis of the VP1 protein gene of foot-and-mouth-disease type C virus allowed us to define optimal stretches whose informative content is not significantly different from that displayed by the complete VP1 sequence. We showed that the predictions made for type C sequences are valid for type O sequences, indicating that the results of the procedure are consistent.
Correspondence to: J. Dopazo 相似文献
16.
Paul N. Adler 《Development genes and evolution》1978,185(3):271-292
Summary Mutations of the bithorax complex result in segmental transformations in the thorax and abdomen ofDrosophila. The haltere discs from larvae homozygous forbx
3 orpbx are transformed so that the discs contain cells that will produce wing cuticle as well as cells that produce haltere cuticle. The pattern regulation behavior of these discs has been examined. The fate maps of the two discs were established, and then the regulative behavior of a number of fragments from both types of mutant discs was established by culturing the fragments in vivo prior to metamorphosis. The most important conclusion from this work is that the cells producing, haltere cuticle and wing cuticle within the same disc share the same positional information and that they communicate during pattern regulation. 相似文献
17.
The asymptotic information in censored survival data 总被引:2,自引:0,他引:2
18.
19.
Robust properties of likelihood ratio tests 总被引:2,自引:0,他引:2
20.
应用地理信息系统模拟森林景观动态的研究 总被引:17,自引:1,他引:16
根据地理信息系统的结构,通过数据文件的转换,把它与森林动态模型有机地结合起来,可实现对森林景观动态的模拟和预测。这种模拟方法的数据输入灵活,运行速度快,尤其是它可以获得一些以各种图表的形式输出的模拟结果。本文用文字和框图详细描述了地理信息系统的组成与结构,及森林动态模型的选择与运行方式,并以长白山森林景观为例,叙述了这种模拟方法的整个过程。 相似文献