A 9-nt segment of a cellular mRNA can function as an internal ribosome entry site (IRES) and when present in linked multiple copies greatly enhances IRES activity
TL;DR: It is shown that increasing the number of copies of this IRES module in the intercistronic region of a dicistronic mRNA strongly enhances IRES activity in various cell lines, and parallels between IRES modules and transcriptional enhancer elements are suggested.
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Abstract: This study addresses the properties of a newly identified internal ribosome entry site (IRES) contained within the mRNA of the homeodomain protein Gtx. Sequential deletions of the 5′ untranslated region (UTR) from either end did not define distinct IRES boundaries; when five nonoverlapping UTR fragments were tested, four had IRES activity. These observations are consistent with other cellular IRES analyses suggesting that some cellular IRESes are composed of segments (IRES modules) that independently and combinatorially contribute to overall IRES activity. We characterize a 9-nt IRES module from the Gtx 5′ UTR that is 100% complementary to the 18S rRNA at nucleotides 1132–1124. In previous work, we demonstrated that this mRNA segment could be crosslinked to its complement within intact 40S subunits. Here we show that increasing the number of copies of this IRES module in the intercistronic region of a dicistronic mRNA strongly enhances IRES activity in various cell lines. Ten linked copies increased IRES activity up to 570-fold in Neuro 2a cells. This level of IRES activity is up to 63-fold greater than that obtained by using the well characterized encephalomyocarditis virus IRES when tested in the same assay system. When the number of nucleotides between two of the 9-nt Gtx IRES modules was increased, the synergy between them decreased. In light of these findings, we discuss possible mechanisms of ribosome recruitment by cellular mRNAs, address the proposed role of higher order RNA structures on cellular IRES activity, and suggest parallels between IRES modules and transcriptional enhancer elements.
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Citations
Quantitative imaging of gene induction in living animals.
X Sun,Alexander J. Annala,Shariar Yaghoubi,Jorge R. Barrio,K N Nguyen,Tatsushi Toyokuni,Nagichettiar Satyamurthy,Mohammad Namavari,M.E. Phelps,Harvey R. Herschman,Sanjiv S. Gambhir +10 more
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IRESdb: the Internal Ribosome Entry Site database
TL;DR: The IRES database is a comprehensive WWW resource for internal ribosome entry sites and presents currently available general information as well as detailed data for each IRES.
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Differential utilization of upstream AUGs in the β-secretase mRNA suggests that a shunting mechanism regulates translation
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Differences in the translation efficiency and mRNA stability mediated by 5'-UTR splice variants of human SP-A1 and SP-A2 genes.
TL;DR: It is found that the hSP-A 5'-UTR splice variants play an important role in both SP-A translation and mRNA stability, and the translational efficiency of each A'D' and A'CD' was lower than that of the control vector.
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Pervasive translation of circular RNAs driven by short IRES-like elements
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