Abstract
Viral protein synthesis is completely dependent upon the host cell's translational machinery. Canonical translation of host mRNAs depends on structural elements such as the 5′ cap structure and/or the 3′ poly(A) tail of the mRNAs. Although many viral mRNAs are devoid of one or both of these structures, they can still translate efficiently using non-canonical mechanisms. Here, we review the tools utilized by positive-sense single-stranded (+ss) RNA plant viruses to initiate non-canonical translation, focusing on cis-acting sequences present in viral mRNAs. We highlight how these elements may interact with host translation factors and speculate on their contribution for achieving translational control. We also describe other translation strategies used by plant viruses to optimize the usage of the coding capacity of their very compact genomes, including leaky scanning initiation, ribosomal frameshifting and stop-codon readthrough. Finally, future research perspectives on the unusual translational strategies of +ssRNA viruses are discussed, including parallelisms between viral and host mRNAs mechanisms of translation, particularly for host mRNAs which are translated under stress conditions.
Highlights
INTRODUCTIONViral mRNA translation is a paradigmatic illustration of this, as the hallmark of viruses is that their genomes do not code for a protein synthesis apparatus
Viruses usurp the metabolism of the host cell in their own benefit
Mechanisms of non-canonical translation initiation include those that function independently of a 5′ cap or/and a poly(A) tail. These can be mediated by stimulators present in cis in the 5′-UTR, for example internal ribosome entry sites (IRESes) or genome-linked viral proteins (VPgs), in the 3′-UTR, for example cap-independent translation elements (3′-CITE) or tRNA-like structures (TLS), and in intergenic regions, for example intergenic IRESes (Table 1)
Summary
Viral mRNA translation is a paradigmatic illustration of this, as the hallmark of viruses is that their genomes do not code for a protein synthesis apparatus. From a strategic point of view, understanding how viruses translate their own proteins may significantly contribute to the identification of therapeutic (Robert et al, 2006; Cencic et al, 2011) or breeding targets (Nicaise et al, 2003; Gao et al, 2004; Ruffel et al, 2005; Stein et al, 2005; Nieto et al, 2006; Naderpour et al, 2010). Describe other protein translation strategies used by plant viruses to optimize the usage of the coding capacity of their very compact genomes, including leaky scanning initiation, ribosomal frameshifting and stop-codon readthrough
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