Nucleic Acids Research Advance Access published online on April 3, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn156
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The poly(A) site sequence in HDV RNA alters both extent and rate of self-cleavage of the antigenomic ribozyme
Department of Biochemistry, Duke University Medical Center, Durham NC 27710, USA
*To whom correspondence should be addressed. Tel: +1 91 9684 2858; Email: mike.been{at}duke.edu
Received November 28, 2007. Revised March 18, 2008. Accepted March 19, 2008.
The ribozyme self-cleavage site in the antigenomic sequence of hepatitis delta virus (HDV) RNA is 33-nt downstream of the poly(A) site for the delta antigen mRNA. An HDV antigenomic ribozyme precursor RNA that included the upstream poly(A) processing site was used to test the hypothesis that nonribozyme sequence near the poly(A) site could affect ribozyme activity. Relative to ribozyme precursor without the extra upstream sequences, the kinetic profile for self-cleavage of the longer precursor was altered in two ways. First, only half of the precursor RNA self-cleaved. The cleaved fraction could be increased or decreased with mutations in the upstream sequence. These mutations, which were predicted to alter the relative stability of competing secondary structures within the precursor, changed the distribution of alternative RNA structures that are resolved in native-gel electrophoresis. Second, the active fraction cleaved with an observed rate constant that was higher than that of the ribozyme without the upstream sequences. Moreover, the higher rate constants occurred at lower, near-physiological, divalent metal ion concentrations (1–2 mM). Modulation of ribozyme activity, through competing alternative structures, could be part of a mechanism that allows a biologically significant choice between maturation of the mRNA and processing of replication intermediates.
Present address: Timothy S. Wadkins, Victory Brewing Co., Downingtown, PA 19335, USA