Cap-independent translation of plant viral RNAs

Abstract

The RNAs of many plant viruses lack a 5′ cap and must be translated by a cap-independent mechanism. Here, we discuss the remarkably diverse cap-independent translation elements that have been identified in members of the Potyviridae, Luteoviridae, and Tombusviridae families, and genus Tobamovirus. Many other plant viruses have uncapped RNAs but their translation control elements are uncharacterized. Cap-independent translation elements of plant viruses differ strikingly from those of animal viruses: they are smaller (<200 nt), some are located in the 3′ untranslated region, some require ribosome scanning from the 5′ end of the mRNA, and the 5′ UTR elements are much less structured than those of animal viruses. We discuss how these elements may interact with host translation factors, and speculate on their mechanism of action and their roles in the virus replication cycle. Much remains to be learned about how these elements enable plant viruses to usurp the host translational machinery.

Eukaryotic Initiation Factor (eIF) 4F Binding to Barley Yellow Dwarf Virus (BYDV) 3′-Untranslated Region Correlates with Translation Efficiency

“…In contrast, BYDV must employ an alternate means of cap-independent translation. Host translation machinery recruitment to the viral mRNA is aided by structures present in 5Ј-and/or 3Ј-UTRs of the mRNAs instead of a 5Ј cap/poly(A) tail (15). For cap-dependent translation initiation, a significant, central role is played by eIF4F.…”

Recruitment of the 40S Ribosome Subunit to the 3′-Untranslated Region (UTR) of a Viral mRNA, via the eIF4 Complex, Facilitates Cap-independent Translation

“…Translation initiation factor eIF4G binds the 3Ј-BTE with high affinity (24,32) and protects SL-I from modification by SHAPE reagents (33). The loop of stemloop III (3Ј-SL-III) of the 3Ј-BTE forms a long distance RNA-RNA "kissing" stem-loop base-pairing interaction with a loop in the 5Ј-end of the mRNA (25,34) (Fig. 1C).…”

Inhibition of Pokeweed Antiviral Protein (PAP) by Turnip Mosaic Virus Genome-linked Protein (VPg)

“…PAP binds to VPg at a different site from the eIFiso4F/eIF4F binding site. The effect of VPg on the depurination of selected RNA molecules, including structured RNA derived from TEV (33)(34)(35), showed that VPg decreases depurination of RNAs and competes with IRES containing TEV RNA for PAP binding. These findings correlate with the inhibition of PAP enzymatic activity by VPg in wheat germ lysate.…”