The 3′ proximal translational enhancer of Turnip crinkle virus binds to 60S ribosomal subunits

Abstract

During cap-dependent translation of eukaryotic mRNAs, initiation factors interact with the 59 cap to attract ribosomes. When animal viruses translate in a cap-independent fashion, ribosomes assemble upstream of initiation codons at internal ribosome entry sites (IRES). In contrast, many plant viral genomes do not contain 59 ends with substantial IRES activity but instead have 39 translational enhancers that function by an unknown mechanism. A 393-nucleotide (nt) region that includes the entire 39 UTR of the Turnip crinkle virus (TCV) synergistically enhances translation of a reporter gene when associated with the TCV 59 UTR. The major enhancer activity was mapped to an internal region of ;140 nt that partially overlaps with a 100-nt structural domain previously predicted to adopt a form with some resemblance to a tRNA, according to a recent study by J.C. McCormack and colleagues. The T-shaped structure binds to 80S ribosomes and 60S ribosomal subunits, and binding is more efficient in the absence of surrounding sequences and in the presence of a pseudoknot that mimics the tRNA-acceptor stem. Untranslated TCV satellite RNA satC, which contains the TCV 39 end and 6-nt differences in the region corresponding to the T-shaped element, does not detectably bind to 80S ribosomes and is not predicted to form a comparable structure. Binding of the TCV T-shaped element by 80S ribosomes was unaffected by salt-washing, reduced in the presence of AcPhe-tRNA, which binds to the P-site, and enhanced binding of Phe-tRNA to the ribosome A site. Mutations that reduced translation in vivo had similar effects on ribosome binding in vitro. This strong correlation suggests that ribosome entry in the 39 UTR is a key function of the 39 translational enhancer of TCV and that the T-shaped element contains some tRNA-like properties.

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

“…A tRNA-shaped 3Ј-CITE of TCV (TSS) was shown to bind directly to the 60S subunit and 80S ribosome, but not the 40S subunit, which leaves the question of how and where the 40S subunit is recruited (29). A TSS-like domain was also found in the 3Ј-UTR of pea enation mosaic virus RNA2 (62), adjacent to another 3Ј-CITE that binds eIF4E (63).…”

“…In addition, plants contain a homolog of eIF4F termed eIF(iso)4F, consisting of eIF(iso)4E and eIF(iso)4G. The tRNA-shaped 3Ј-CITE of turnip crinkle virus binds directly to ribosomal 60S subunits and 80S ribosomes, but its interactions with initiation factors are unknown (29). The factor requirements of the most recently discovered 3Ј-CITE (from the Xinjiang isolate of Cucurbit aphid-borne yellows virus) are also unknown (30).…”

Mimicry of molecular pretenders: The terminal structures of satellites associated with plant RNA viruses

“…18 In TCV, H4a loop sequences interact with upstream flanking sequences to form another pseudoknot (ψ3), which is functional in translation. 19 However, the formation of ψ3 is not important for non translated satC replication. In vivo genetic selection results revealed that satTCV H4a and H4b contain alternative structures in function to that of the wild type, which suggests that satC RNAs develop distinct elements to achieve similar functions.…”

Análisis Funcional De Proteínas Codificadas Por El Virus De La Rotura Del Color De La Flor Del Pelargonium

“…in Figs 3 and 4). The structural features that distinguish the two conformations of the ssRNA probe are not currently known, but it is probable that they are the result of the adoption of distinct higher-order structures similar to those described in the 3'-terminal region of other members of the Tombusviridae [McCormack et al, 2008;Na & White, 2006;Pogany et al, 2003;Wang & Wong, 2004] and also predicted in PFBV . Though RNA-binding properties have not been described so far for p27 homologues of other carmoviruses, the p27-binding capability parallels the results obtained with the equivalent replicase protein of TBSV, p33, the only related protein for which this question has been investigated [Rajendran & Nagy, 2003].…”

“…Además de los elementos implicados en la replicación, se ha descrito la presencia de reguladores traduccionales en la 3´ UTR de distintos miembros de la familia Tombusviridae que parecen promover una traducción eficiente de los vRNA en ausencia de estructuras cap Stupina et al, 2008;Truniger et al, 2008;Wang et al, 2011b].…”