Parallelism, It\u27s Evolutionary Origin and Systematic Significance

Parallelism as one of the forms of biological similarity is investigated in the light of recent findings from developmental and molecular biology. From the organismic point of view, functional constraints and evolutionary canalization are well established as causes of parallelism. To these may be added, from the molecular perspective, (a) erratic activations of repressed genes; (b) activations of alternative pathways under the influence ofhomoeotic genes; and (c) horizontal gene transfer, for which a simple mechanism is proposed. The control of gene expression through the action oftransposable elements, reversible to some degree, appears to be an evolutionarily important and frequent phenomenon, which may account for many cases formerly interpreted as losses or irreversible changes of genes. It is suggested that this mechanism, which seems to be optimized in angiosperms, may account for the great evolutionary plasticity of this plant group. It may also provide an explanation for so-called reversals which appear as artifacts of character analyses and are biologically barely explicable. Events of horizontal gene transfer, creative for evolution but disturbing for classification, appear less frequent, or otherwise the structure of the taxonomic hierarchy would not be perceptible. Increasing knowledge in the fields of molecular and developmental biology tends to blur the borderline between homology, homoiology, parallelism, and perhaps convergence, phenomena formerly thought to be more or less distinct

Über die Vegetationsentwicklung des Weichsel-Interstadials aus Hamburg-Bahrenfeld

Eine interstadiale, aus Gyttja und Torfen aufgebaute Lagefolge, die mit dem aus Dänemark und Holland beschriebenen Brörup-Interstadial parallelisiert wird, wurde pollenanalytisch und z. T. hinsichtlich ihrer Makroflora untersucht. Danach ergibt sich der waldlose bis waldarme, durch Vorwalten von Zwergbirken und krautigen Pflanzen gekennzeichnete Abschnitt I und der Abschnitt II mit großer Bewaldungsdichte, in dem offenbar zunächst Birken und schließlich Kiefern und Fichten die Wälder beherrschten, während die lokale Moorvegetation ihr Gepräge durch das gleichzeitige Vorkommen von Zwergbirken und Bergkiefern erhielt, dessen pflanzengeographische Bedeutung gewürdigt wird.researc

Minimum Free Energy Path of Ligand-Induced Transition in Adenylate Kinase

Large-scale conformational changes in proteins involve barrier-crossing transitions on the complex free energy surfaces of high-dimensional space. Such rare events cannot be efficiently captured by conventional molecular dynamics simulations. Here we show that, by combining the on-the-fly string method and the multi-state Bennett acceptance ratio (MBAR) method, the free energy profile of a conformational transition pathway in Escherichia coli adenylate kinase can be characterized in a high-dimensional space. The minimum free energy paths of the conformational transitions in adenylate kinase were explored by the on-the-fly string method in 20-dimensional space spanned by the 20 largest-amplitude principal modes, and the free energy and various kinds of average physical quantities along the pathways were successfully evaluated by the MBAR method. The influence of ligand binding on the pathways was characterized in terms of rigid-body motions of the lid-shaped ATP-binding domain (LID) and the AMP-binding (AMPbd) domains. It was found that the LID domain was able to partially close without the ligand, while the closure of the AMPbd domain required the ligand binding. The transition state ensemble of the ligand bound form was identified as those structures characterized by highly specific binding of the ligand to the AMPbd domain, and was validated by unrestrained MD simulations. It was also found that complete closure of the LID domain required the dehydration of solvents around the P-loop. These findings suggest that the interplay of the two different types of domain motion is an essential feature in the conformational transition of the enzyme