Zum Problem der Stabilität der Klimabedingungen in Westsibirien während der Glaziale und Interglaziale

Es werden zunächst Werte für die sommerliche Temperaturerniedrigung und für den jährlichen Temperaturgang während der letzten Eiszeit in Westsibirien abgeleitet. Grundlage hierfür bildet die verschiedene Lage der Grenzen von Tundra und Laubmischwald zur Eiszeit (nach Frenzel & Troll 1952) und in der Gegenwart (Sowjetatlas 1937). Das Ergebnis ist eine sommerliche Temperaturdepression von nur 5-8° C nahe dem Polarkreis und von 2-4° C in 50° Breite gegenüber 10-12° in Mitteleuropa. Anschließend wird die Frage diskutiert, ob dies allein eine Folge der größeren Kontinentalität des zentralen Teiles Eurasiens gegenüber dem westlichen und östlichen Teil des Doppelkontinentes sein kann. Es stellt sich heraus, daß die relative Stabilität der Klimabedingungen Westsibiriens im ganzen Quartär sich zwanglos als Folge des Wechsels von vorherrschender Meridionalzirkulation im Glazial und verstärkter Zonalzirkulation im Interglazial und Postglazial erklären läßt.researc

The Role of Oligomerization and Cooperative Regulation in Protein Function: The Case of Tryptophan Synthase

The oligomerization/co-localization of protein complexes and their cooperative regulation in protein function is a key feature in many biological systems. The synergistic regulation in different subunits often enhances the functional properties of the multi-enzyme complex. The present study used molecular dynamics and Brownian dynamics simulations to study the effects of allostery, oligomerization and intermediate channeling on enhancing the protein function of tryptophan synthase (TRPS). TRPS uses a set of α/β–dimeric units to catalyze the last two steps of L-tryptophan biosynthesis, and the rate is remarkably slower in the isolated monomers. Our work shows that without their binding partner, the isolated monomers are stable and more rigid. The substrates can form fairly stable interactions with the protein in both forms when the protein reaches the final ligand–bound conformations. Our simulations also revealed that the α/β–dimeric unit stabilizes the substrate–protein conformation in the ligand binding process, which lowers the conformation transition barrier and helps the protein conformations shift from an open/inactive form to a closed/active form. Brownian dynamics simulations with a coarse-grained model illustrate how protein conformations affect substrate channeling. The results highlight the complex roles of protein oligomerization and the fine balance between rigidity and dynamics in protein function

Protection of expressed immunoglobulin genes against nuclease cleavage.

Fragmentation of the actively transcribed kappa immunoglobulin gene in mouse myeloma nuclei with micrococcal nuclease and the restriction nuclease Bsp RI reveals a chromatin structure without the regularity of repeating nucleosomes found in bulk chromatin. Such regularity is restored about 2.2 kb 3' of the coding region. An only moderately increased micrococcal nuclease sensitivity and a 65% average protection of the Bsp RI sites indicates a DNA-protein interaction in the transcribed region which is not very different from that of an inactive gene. As determined by indirect endlabeling the frequency of Bsp RI cleavage both, after very mild and exhaustive digestion, varied moderately from site to site along the gene. In addition, it was not in each case the same at analogous sites on both alleles which are both transcribed. Thus, the experiments demonstrate differences between the chromatin structures of the genes which may be related to regulatory phenomena and thereby corroborate earlier findings made with DNAase I