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  • 1
    ISSN: 1434-4475
    Keywords: RNA secondary structures ; RNA free energies ; Value landscapes ; Autocorrelation functions ; Correlation lengths
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung RNA-Sekundärstrukturen werden aus den Primärsequenzen mit Hilfe eines Computeralgorithmus berechnet, welcher einem Kriterium minimaler freier Energien folgt. Freie Energien, Replikations- oder Abbaugeschwindigkeitskonstanten werden aus den Sekundärstrukturen berechnet. Man kann daher diese Eigenschaften als komplizierte Funktionen der Sequenzen auffassen, deren Zahlenwerte durch Vermittlung der Sekundärstrukturen erhalten werden. Diese Funktionen induzieren hochkomplexe Bewertungslandschaften im Raum der Sequenzen. Die Landschaften werden mit Hilfe von Irrflugtechniken analysiert. Im einzelnen werden Autokorrelationsfunktionen und Korrelationslängen berechnet. Die freien Energie-Landschaften sind vom AR(1) Typ. Die von den Reaktionsgeschwindigkeitskonstanten abgeleiteten Landschaften stellten sich hingegen als komplexer heraus. Zusätzlich werden die Bewertungslandschaften auch noch mit Hilfe vonGradient undAdaptive Walks untersucht, um mehr Einblick in ihre komplexe Struktur zu gewinnen.
    Notes: Summary RNA secondary structures are computed from primary sequences by means of a folding algorithm which uses a minimum free energy criterion. Free energies as well as replication and degradation rate constants are derived from secondary structures. These properties can be understood as highly sophisticated functions of the individual sequences whose values are mediated by the secondary structures. Such functions induce complex value landscapes on the space of sequences. The landscapes are analysed by random walk techniques, in particular autocorrelation functions and correlation lengths are computed. Free energy landscapes were found to be of AR(1) type. The rate constant landscapes, however, turned out to be more complex. In addition, gradient and adaptive walks are performed in order to get more insight into the complex structure of the landscapes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1017
    Keywords: Key words RNA structural motifs ; GNRA tetraloops ; Conformational search ; Solvent effects ; Electrostatic continuum model ; AbbreviationsMC-SYM Macromolecular conformations by symbolic programming ; JUMNA Junction minimization of nucleic acids ; AMBER Assisted model building with energy refinement ; RF Reaction field ; FIESTA Field integrated electrostatic approach ; FD Finite difference ; sc Synclinal ; ac Anticlinal ; ap Antiperiplanar ; ED Electrostatic damping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The protocol of conformational analysis applied here to ribonucleotide oligomers combines conformational search in the space of torsion angles and energy minimization using the AMBER4.1 force field with a continuum treatment of electrostatic solute-solvent interactions. RNA fragments with 5′-GGGCGNNAGCCU-3′ sequences commonly fold into hairpins with four-membered loops. The combinatorial search for acceptable conformations using the MC-SYM program was restricted to loop nucleotides and yielded roughly 1500 structures being compatible with a double-stranded stem. After energy minimization by the JUMNA program (without applying any experimental constraints), these structures converged into an ensemble of 74 different conformers including 26 structures which contained the sheared G-A base pair observed in experimental studies of GNRA tetraloops. Energetic analysis shows that inclusion of solvent electrostatic effects is critically important for the selection of conformers that agree with experimentally determined structures. The continuum model accounts for solvent polarization by means of the electrostatic reaction field. In the case of GNRA loop sequences, the contributions of the reaction field shift relative stabilities towards conformations showing most of the structural features derived from NMR studies. The agreement of computed conformations with the experimental structures of GAAA, GCAA, and GAGA tetraloops suggests that the continuum treatment of the solvent represents a definitive improvement over methods using simple damping models in electrostatic energy calculations. Application of the procedure described here to the evaluation of the relative stabilities of conformers resulting from searching the conformational space of RNA structural motifs provides some progress in (non-homology based) RNA 3D-structure prediction.
    Type of Medium: Electronic Resource
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