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  • Title: Effects of substrate structure on the kinetics of circle opening reactions of the self-splicing intervening sequence from Tetrahymena thermophila: evidence for substrate and Mg2+ binding interactions.
    Author: Sugimoto N, Tomka M, Kierzek R, Bevilacqua PC, Turner DH.
    Journal: Nucleic Acids Res; 1989 Jan 11; 17(1):355-71. PubMed ID: 2643083.
    Abstract:
    The self-splicing intervening sequence from the precursor rRNA of Tetrahymena thermophila cyclizes to form a covalently closed circle. This circle can be reopened by reaction with oligonucleotides or water. The kinetics of circle opening as a function of substrate and Mg2+ concentrations have been measured for dCrU, rCdU, dCdT, and H2O addition. Comparisons with previous results for rCrU suggest: (1) the 2' OH of the 5' sugar of a dinucleoside phosphate is involved in substrate binding, and (2) the 2' OH of the 3' sugar of a dimer substrate is involved in Mg2+ binding. Evidently, the binding site for a required Mg2+ ion is dependent on both the ribozyme and the dimer substrate. The apparent activation energy and entropy for circle opening by hydrolysis are 31 kcal/mol and 50 eu, respectively. The large, positive activation entropy suggests a partial unfolding of the ribozyme is required for reaction.
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