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# A Labile Phosphodiester Bond at the Ligation Junction in a Circular Intervening Sequence RNA

Arthur J. Zaug, Jeffrey R. Kent and Thomas R. Cech
Science
New Series, Vol. 224, No. 4649 (May 11, 1984), pp. 574-578
Stable URL: http://www.jstor.org/stable/1692906
Page Count: 5
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## Abstract

The excised intervening sequence of the Tetrahymena ribosomal RNA precursor mediates its own covalent cyclization in the absence of any protein. The circular molecule undergoes slow reopening at a single phosphodiester bond, the one that was formed during cyclization. The resulting linear molecular has 5$^{\prime}$-phosphate and 3$^{\prime}$-hydroxyl termini; these are unusual products for RNA hydrolysis but are typical of the other reactions mediated by this molecule. The reopened circle retains cleavage-ligation activity, as evidenced by its ability to undergo another round of cyclization and reopening. The finding that an RNA molecule can be folded so that a specific phosphate can be strained or activated helps to explain how the activation energy is lowered for RNA self-splicing. The proposed mechanisms may be relevant to several other RNA cleavage reactions that are RNA-mediated.

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