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
AUTOR(ES)
Chappell, Stephen A.
FONTE
The National Academy of Sciences
RESUMO
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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=26470Documentos Relacionados
- Pestivirus Internal Ribosome Entry Site (IRES) Structure and Function: Elements in the 5′ Untranslated Region Important for IRES Function
- Inherent Instability of Poliovirus Genomes Containing Two Internal Ribosome Entry Site (IRES) Elements Supports a Role for the IRES in Encapsidation
- Hepatitis C Virus Internal Ribosome Entry Site (IRES) Stem Loop IIId Contains a Phylogenetically Conserved GGG Triplet Essential for Translation and IRES Folding
- In vitro characterization of an internal ribosomal entry site (IRES) present within the 5' nontranslated region of hepatitis A virus RNA: comparison with the IRES of encephalomyocarditis virus.
- Translation of NRF mRNA Is Mediated by Highly Efficient Internal Ribosome Entry