Effects of antisense oligodeoxynucleotide hybridization on in vitro translation of potato virus Y RNA

The Additional 15 nt of 5' UTR in a Novel Recombinant Isolate of Chilli Veinal Mottle Virus in Solanum nigrum L. Is Crucial for Infection

An isolate of chilli veinal mottle virus (ChiVMV; genus Potyvirus) of Solanum nigrum L. from southwest China (ChiVMV-YunN/Yuxi) was identified and sequenced (GenBank: OP404087). Comparison with other ChiVMV isolates and recombination analyses suggested a recombinant origin. The most significant recombination event among all 21 complete ChiVMV isolates was an ending breakpoint at 1408-1488 for ChiVMV-YunN/Yuxi with ChiVMV-TaiW and ChiVMV-YunN/Ca operating as the respective major and minor parents. Interestingly, the 5' UTR of ChiVMV-YunN/Yuxi is 15 nucleotides ('AAAAATAAAACAACC') longer than other reported isolates. A full-length clone of ChiVMV-YunN/Yuxi was constructed and was shown to be infectious in Nicotiana benthamiana. The additional 15 nt of 5' UTR in ChiVMV-YunN/Yuxi was stable when transmitted through three generations. Experiments with modified clones showed that the additional 15 nt are essential for infection by this isolate.

The potential exploitation of plant viral translational enhancers in biotechnology for increased gene expression

The regulation of gene expression is extremely important for all organisms, not least for viruses that require a maximum rate of production of viral proteins to allow rapid multiplication and spread. Single-stranded positive-sense RNA viruses contain specific nucleotide sequences that can be used to elevate the expression of vital gene products to required high levels. Among plant viruses, translational enhancement has been documented widely, especially over the past few years. Reported candidates include one of the best known and most intensely researched virus, tobacco mosaic virus, members of the potyvirus group, and even a small satellite RNA of tobacco necrosis virus. Enhancement values range from 2-100-fold with different viruses, different reporter genes, and in different systems. Research indicates that an absence of secondary structure alone does not explain translational enhancement and despite attempts to determine the mechanism by which this enhancement occurs very little conclusions can be made as yet. Whatever the mechanism, the presence of these sequences upstream from an open reading frame results in an elevated level of protein production and may feature as important tools for biotechnology in the future.

The role of the 5' untranslated region of eukaryotic messenger RNAs in translation and its investigation using antisense technologies

This chapter discusses the recent advances in the field of translational control and the possibility of applying the powerful antisense technology to investigate some of the unanswered questions, especially those pertaining to the role of the 5’untranslated region ( UTR) on translation initiation. Translational regulation is predominantly exerted during the initiation phase that is considered to be the rate-limiting step. Two types of translational regulation can be distinguished: global, in which the initiation rate of (nearly) all cellular messenger RNA (mRNA) is controlled and selective, in which the translation rate of specific mRNAs varies in response to the biological stimuli. In most cases of global regulation, control is exerted via the phosphorylation state of certain initiation factors, whereas only a few examples of selective regulation have been characterized well enough to define the underlying molecular events. Interestingly, cis-acting regulatory sequences, affecting translation initiation, have been found not only in the 5’UTRs of selectively regulated mRNAs, but also in the 3’UTRs. Thus, in addition to the protein encoding open reading frames, both the 5’ and 3’UTRs of mRNAs must be considered for their effect on translation.

The 5' untranslated region of PVY RNA, even located in an internal position, enables initiation of translation

Potato virus Y (PVY) is the type member of the potyvirus group. Potyviruses, like picorna-, como-, and nepoviruses, belong to the picornavirus-like supergroup. All these viral RNAs have a VPg at their 5' end, and for four picornaviruses and one comovirus internal initiation of translation has been reported. To know if such a translational mechanism holds true for potyviral RNAs, the 5' nontranslated region (NTR) of PVY RNA was placed in an internal position, either by adding 91 bases upstream of the PVY 5'NTR or by inserting the PVY 5'NTR into an intercistronic region. The addition of extra bases stimulates translation in a rabbit reticulocyte lysate, and the presence of the PVY 5'NTR in the intercistronic region allows the synthesis of the second cistron. These findings strongly suggest that PVY RNA initiates translation by an internal ribosome-binding mechanism. Furthermore, the use of antisense oligodeoxynucleotides indicates that the entire 5'NTR seems to be involved in such a mechanism.