A viral sequence in the 3′-untranslated region mimics a 5′ cap in facilitating translation of uncapped mRNA

Abstract

For recognition by the translational machinery, most eukaryotic cellular mRNAs have a 5' cap structure [e.g. m7G(5')ppp(5')N]. We describe a translation enhancer sequence (3'TE) located in the 3'-untranslated region (UTR) of the genome of the PAV barley yellow dwarf virus (BYDV-PAV) which stimulates translation from uncapped mRNA by 30- to 100-fold in vitro and in vivo to a level equal to that of efficient capped mRNAs. A four base duplication within the 3'TE destroyed the stimulatory activity. Efficient translation was recovered by addition of a 5' cap to this mRNA. Translation of both uncapped mRNA containing the 3'TE in cis and capped mRNA lacking any BYDV-PAV sequence was inhibited specifically by added 3'TE RNA in trans. This inhibition was reversed by adding initiation factor 4F (eIF4F), suggesting that the 3'TE, like the 5' cap, mediates eIF4F-dependent translation initiation. The BYDV-PAV 5'UTR was necessary for the 3'TE to function, except when the 3'TE itself was moved to the 5'UTR. Thus, the 3'TE is sufficient for recruiting the translation factors and ribosomes, while the viral 5'UTR may serve only for the long distance 3'-5' communication. Models are proposed to explain this novel mechanism of cap-independent translation initiation facilitated by the 3'UTR.

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

“…BLucB-SL-Dm1 is a mutated BLucB plasmid where CUGA-CAA nucleotides of stem-loop D (5Ј-SL-D) were mutated to CUGUCAA to disrupt the "kissing loop" interaction. Preparation and construction of these plasmids were described previously (23,31,35). BYDV 5Ј-UTR plasmid in a pUC MINUS MCS form was constructed by Blue Heron Biotechnology, Inc. (Bothell, WA) and was also used for in vitro study.…”

“…In the 17-nt CS, bases 2-7 (GAUCCU) (Fig. 1) are complementary to a tract near the 3Ј-end of 18S rRNA at the site where the Shine-Dalgarno complementary sequence is located in prokaryotic ribosomes (31). However, the terminal three bases (underlined) are base-paired within the 17-nt CS (Fig.…”

“…1, the bases in italic type are the CS, and those in the green box are complementary to a sequence near the 3Ј-end of 18S rRNA (Fig. 1B) (31). Translation initiation factor eIF4G binds the 3Ј-BTE with high affinity (24,32) and protects SL-I from modification by SHAPE reagents (33).…”

A Novel Interaction of Cap-binding Protein Complexes Eukaryotic Initiation Factor (eIF) 4F and eIF(iso)4F with a Region in the 3′-Untranslated Region of Satellite Tobacco Necrosis Virus

“…Wang and Miller (38) previously identified a cap-independent translational enhancer (TE) domain located within the 3Ј-UTR of BYDV. The TE stimulates translation of viral and heterologous genes 30 -100-fold (38), and inactivation of this enhancer region renders BYDV RNA cap-dependent (37,39). The addition of the BYDV TE domain in trans specifically inhibits in vitro translation and is reversed by the addition of eIF4F (39).…”

“…The TE stimulates translation of viral and heterologous genes 30 -100-fold (38), and inactivation of this enhancer region renders BYDV RNA cap-dependent (37,39). The addition of the BYDV TE domain in trans specifically inhibits in vitro translation and is reversed by the addition of eIF4F (39). The BYDV TE has been shown to interact through base pairing with a stem-loop located in the 5Ј-UTR (40,41), serving as a way for the viral RNA to bring the 5Ј-and 3Ј-UTRs into contact mimicking the eIF4G-PABP interaction.…”