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Molecular and Cellular Biology, September 2000, p. 6212-6223, Vol. 20, No. 17
Friedrich Miescher Institute, CH-4058 Basel,
Switzerland,1 and Gene Expression
Program, EMBL, D-69117 Heidelberg, Germany2
Received 1 March 2000/Returned for modification 17 April
2000/Accepted 30 May 2000
We have shown recently that a stable hairpin preceded by a short
upstream open reading frame (uORF) promotes nonlinear ribosome migration or ribosome shunt on a synthetic mRNA leader (M. Hemmings-Mieszczak and T. Hohn, RNA 5:1149-1157, 1999). We have now
used the model mRNA leader to study further the mechanism of
shunting in vivo and in vitro. We show that a full cycle of translation
of the uORF, including initiation, elongation, and termination, is a precondition for the ribosome shunt across the stem structure to
initiate translation downstream. Specifically, AUG recognition and the proper release of the nascent peptide are necessary and sufficient for shunting. Furthermore, the stop codon context must not
impede downstream reinitiation. Translation of the main ORF was
inhibited by replacement of the uORF by coding sequences
repressing reinitiation but stimulated by the presence of the
virus-specific translational transactivator of reinitiation
(cauliflower mosaic virus pVI). Our results indicate reinitiation as
the mechanism of translation initiation on the synthetic
shunt-competent mRNA leader and suggest that uORF-dependent
shunting is more prevalent than previously anticipated. Within the
above constraints, uORF-dependent shunting is quite tolerant of uORF
and stem sequences and operates in systems as diverse as plants and fungi.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Termination and Peptide Release at the Upstream Open Reading
Frame Are Required for Downstream Translation on Synthetic
Shunt-Competent mRNA Leaders
*
Corresponding author. Mailing address: Friedrich
Miescher Institute, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.
Phone: 41 61 6976684. Fax: 41 61 6973976. E-mail:
mieszcza{at}fmi.ch.
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