Nucleic Acids Research, Vol 25, Issue 11 2189-2196, Copyright © 1997 by Oxford University Press
O Mitrasinovic and LM Epstein
The hammerhead self-cleaving motif occurs in a variety of RNAs that infect
plants and consists of three non-conserved helices connected by a highly
conserved central core. A variant hammerhead, called the extended
hammerhead, is found in satellite 2 transcripts from a variety of caudate
amphibians. The extended hammerhead has the same core as the prototypical
hammerhead, but has unusually conserved sequence and structural elements in
its peripheral helices. Here we present the results of a thiophosphate
substitution interference analysis of the pro-Rp phosphate oxygen
requirements in the two hammerhead forms. Five pro-Rp phosphate oxygens,
all in the central core, were found to be important for self-cleavage by
the prototypical hammerhead. A similar set of core positions were important
for self-cleavage by the extended hammerhead, but five non-core positions
were also found to be important. Thiosubstitution at one of these positions
had the most severe effect on self-cleavage observed in this analysis. Mn2+
did not alleviate this negative effect, indicating that this position was
not part of a divalent cation binding site. We propose that novel tertiary
interactions in the extended hammerhead help form the same catalytic core
structure as that used by the prototypical plant virus hammerhead.
ARTICLES
Differences in the phosphate oxygen requirements for self-cleavage by the extended and prototypical hammerhead forms
Department of Chemistry, Florida State University, Tallahassee, FL 32306-3050, USA.
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