Structure/Function Analysis of the TEV IRES and its Interaction With eIF4G, eIF4A, and eIF4B

University Of California-Riverside, Riverside CA

Investigators

Abstract

Tobacco etch virus (TEV) is a potyvirus, a member of the picornavirus supergroup of positive-strand RNA viruses, which infects plants. Like encephalomyocarditis virus (EMCV) and poliovirus, the genomic RNA of TEV is a polyadenylated mRNA that naturally lacks a 5' cap structure but is nevertheless efficiently translated. The TEV 5'-leader is sufficient to confer cap-independent translation to an mRNA and it is functionally analogous to a cap in that it interacts with the poly(A) tail to promote efficient translation. The TEV 5'-leader also promotes translation of the 5'-distal (i.e., second) cistron of a dicistronic mRNA in vivo when it is present in the intercistronic region, an observation indicating that the TEV 5'-leader functions as an internal ribosome entry site (IRES). The translation initiation factor eIF4G is required for TEV IRES function. The mechanism underlying IRES-mediated cap-independent translation has not been investigated for TEV or any other plant virus. The observation that the TEV is a naturally uncapped mRNA that has evolved a 5'-leader sequence that confers cap-independent translation, functions even when positioned in the intercistronic region of a dicistronic mRNA to promote internal initiation, and requires eIF4G for IRES function suggests that this member of the picornaviral superfamily may share similarities to IRES function described for animal picornaviruses such as EMCV and FMDV. The goal of this project is to determine the mechanism by which TEV IRES function promotes cap-independent translation in plants. This project will be the first to establish whether a plant viral IRES functions like animal picornaviral IRES. Because of the mechanistic differences among animal picornaviral IRESs, the research will determine whether the evolution of the TEV IRES is more similar to the IRES of EMCV (which can recruit eIF4G directly) or poliovirus (which may require the assistance of other factors to recruit eIF4G). The research will determine the structure of the TEV IRES and investigate whether eIF4G binds directly or is recruited to the TEV IRES by an additional trans-acting factor. The IRES of TEV is substantially smaller than animal picornaviral IRESs, suggesting that an IRES does not require extensive sequence to recruit the translational machinery. Elucidation of how such a simplified IRES can efficiently recruit the translational machinery in a cap-independent manner will provide important insight into the minimum requirement for IRES function in a higher eukaryote.