Mutational Analysis of the Bovine Hepacivirus Internal Ribosome Entry Site

ABSTRACTIn recent years, hepatitis C virus (HCV)-related viruses were identified in several species, including dogs, horses, bats, and rodents. In addition, a novel virus of the genusHepacivirushas been discovered in bovine samples and was termed bovine hepacivirus (BovHepV). Prediction of the BovHepV internal ribosome entry site (IRES) structure revealed strong similarities to the HCV IRES structure comprising domains II, IIIabcde, pseudoknot IIIf, and IV with the initiation codon AUG. Unlike HCV, only one microRNA-122 (miR-122) binding site could be identified in the BovHepV 5′ nontranslated region. In this study, we analyzed the necessity of BovHepV IRES domains to initiate translation and investigated possible interactions between the IRES and core coding sequences by using a dual luciferase reporter assay. Our results suggest that such long-range interactions within the viral genome can affect IRES-driven translation. Moreover, the significance of a possible miR-122 binding to the BovHepV IRES was investigated. When analyzing translation in human Huh-7 cells with large amounts of endogenous miR-122, introduction of point mutations to the miR-122 binding site resulted in reduced translation efficiency. Similar results were observed in HeLa cells after substitution of miR-122. Nevertheless, the absence of pronounced effects in a bovine hepatocyte cell line expressing hardly any miR-122 as well suggests additional functions of this host factor in virus replication.IMPORTANCESeveral members of the familyFlaviviridae, including HCV, have adapted cap-independent translation strategies to overcome canonical eukaryotic translation pathways and usecis-acting RNA-elements, designated viral internal ribosome entry sites (IRES), to initiate translation. Although novel hepaciviruses have been identified in different animal species, only limited information is available on their biology on molecular level. Therefore, our aim was a fundamental analysis of BovHepV IRES functions. The findings which show that functional IRES elements are also crucial for BovHepV translation expand our knowledge on molecular mechanism of hepacivirus propagation. We also studied the possible effects of one major host factor implicated in HCV pathogenesis, miR-122. The results of mutational analyses suggested that miR-122 enhances virus translation mediated by BovHepV IRES.

Complete Genome Sequence of a Sub-Subgenotype 2.1i Isolate of Classical Swine Fever Virus from China

ABSTRACT The complete genome sequence of a sub-subgenotype 2.1i isolate of classical swine fever virus (CSFV), GD317/2011, was determined. Notably, GD317/2011 is distant from the sub-subgenotype 2.1b isolate HEBZ at genes of Erns, E1, E2, P7, NS2, NS5A and the 3′-nontranslated region (3′-NTR) but is closely related to that at genes of Npro, Core, NS3, NS4A, NS4B, and NS5B.

First Report of Wild tomato mosaic virus Infecting Tobacco (Nicotiana tabacum) in China

Wild tomato mosaic virus (WTMV), a potyvirus, has been reported in Laichau, Vietnam, infecting Solanum torvum (wild tomato) in 2008 (3), and Kanchanaburi, Thailand, infecting Capsicum spp. in 2013 (KF250353). In mid-May 2013, Nicotiana tabacum showing yellowing, mosaic, and/or ringspot symptoms were found in natural tobacco fields of Nanxiong, Guangdong Province, China. Total RNA was extracted from symptomatic leaves and reverse transcribed with M4T (5′-GTTTTCCCAGTCACGAC (T)15-3′) as the 3′ anchoring primer (1). The cDNA was used as template in a PCR assay using primers M4: 5′-GTTTTCCCAGTCACGAC-3′ and Sprimer: 5′-GGXAAYAAYAGYGGXCAZCC-3′, which amplifies a region comprising part of the NIb protein gene, the entire coat protein (CP) gene and the 3′ nontranslated region (UTR) of a potyvirus (1). A ~1,700-bp product was amplified from the cDNA derived from three of the five diseased plants. The product (KF639967) showed 87% and 84% nucleotide sequence identities with those of WTMV isolates KAN and Laichau, respectively. The CP deduced from the sequence of the product shared 87% and 86% nucleotide and 94% and 93% amino acid sequence identities with those of WTMV isolates KAN and Laichau, respectively. The 3′-UTR of the putative virus shared 93% and 92% nucleotide sequence identities to those of WTMV isolates KAN and Laichau, respectively. Thus, according to the molecular criteria for potyvirus species demarcation (2), the virus we identified should be an isolate of WTMV (isolate GD1). One of the diseased samples was homogenized in 0.1 mol/liter phosphate buffer (pH 7.0) and used to inoculate the potyvirus to healthy, two to four leaf-stage Capsicum annuum L., N. tabacum, and N. benthamiana. The inoculated, as well as mock-treated plants, which were inoculated only with phosphate buffer, were grown in soil under 12 h day/12 h night at 25°C. All inoculated N. tabacum and N. benthamiana plants developed yellowing and mosaic symptoms by 14 days post inoculation (dpi). For N. benthamiana, the symptom became very severe by 21 dpi and some diseased plants died prematurely. About 10% of inoculated C. annuum L. developed very mild veinal chlorosis 18 dpi. Cloning and sequencing experiments showed that all the symptomatic plants tested were WTMV positive, but Cucumber mosaic virus, Tobacco mosaic virus, and Tobacco etch virus negative. To our knowledge, this is the first report of WTMV in China. Also, it is the first report that WTMV infects Nicotiana spp. Although further experiments are needed to definitively attribute the disease observed in the field to WTMV, our results indicate that WTMV, which forms a monophyletic clade with a number of other potyviruses infecting Solanaceae species in phylogenetic analysis, is widely distributed, or is spreading in Southeast Asia. It may pose a threat to Solanaceae species cultivation in this region. References: (1) Chen et al. Arch. Virol. 146:757, 2001. (2) Adams et al. Arch. Virol. 150:459, 2005. (3) Ha et al. Arch. Virol. 153:25, 2008.

First Report of Johnsongrass mosaic virus (JGMV) Infecting Pennisetum purpureum in Brazil

Tropical grass and legume species used as pasture grasses for cattle feeding cover over 25% of the agricultural area in Brazil. In recent years, plants showing virus-like symptoms have been observed in the main pasture grass growing areas. Plants of Pennisetum purpureum line CNPGL 00211 showing typical virus mosaic symptoms on leaves and growth reduction were collected in Bahia State, Brazil. Flexuous elongated potyvirus-like particles were observed in the leaf-dip preparation of diseased plants by electron microscopy. In addition, the virus was mechanically transmitted using a standard procedure for potyviruses (4) and produced similar symptoms in inoculated P. purpureum plants. For further molecular identification, total RNA was extracted from frozen symptomatic leaves following the guanidine thiocyanate method (3). cDNA synthesis was performed using oligonucleotide, OligodT50M10 and PCR was carried out using Potyvirus degenerate primers PY11 (5′-GGNAAYAAYAGYGGNCARCC-3′) (2) and M10 (5′-AAGCAGTGTTATCAACGCAGA-3′). The amplified fragments of the expected size (approximately 2 kb comprising part of the NIb protein gene, the entire coat protein [CP] gene, and the 3′ nontranslated region) were separated using agarose gel electrophoresis, excised, and cloned into plasmid vector pGEMT-Easy (Promega) according to the manufacturer's instructions. Four selected clones were sequenced (Macrogen, South Korea). The sequenced 2.0-kb fragment (GenBank Accession No. KC333416) was compared with sequences available in GenBank and the highest nucleotide identity of 79% was observed with Johnsongrass mosaic virus (JGMV) isolated in Australia (4). According to the Potyvirus species demarcation convention based on CP identity (1), the virus isolate from P. purpureum belongs to the JGMV species. However, the amino acid sequence of the N-terminus of the CP of the Bahia isolate is distinct from JGMV sequences reported in GenBank. The phylogenetic analysis of the CP confirmed the difference since this Bahia isolate was located in a clearly distinct branch separate from all JGMV isolates. To our knowledge, this is the first report of a JGMV in Brazil infecting tropical grass in the main pasture areas. References: (1) M. J. Adams et al. Arch. Virol. 150: 459, 2005. (2) J. Chen et al. Arch. Virol. 146:757. 2001. (3) P. Chomczynski and N. Sacchi. Nature Protocols 1:581, 2006. (4) H. K. Laidlaw et al. Arch. Virol. 149:1633, 2004.

Molecular and Biological Characterization of Chinese Sacbrood Virus LN Isolate

Chinese sacbrood virus (CSBV) was purified from diseased insects, and its genome was cloned and sequenced. The genomic RNA of CSBV is 8863 nucleotides in length and contains a single large open reading frame encoding a 319.614 kDa polyprotein. The coding sequence is flanked by a 178-nucleotide 5′nontranslated leader sequence and a 142-nucleotide 3′nontranslated region, followed a poly(A) tail. Four major structural proteins, VP1,VP2, VP3 and VP4, were predicted in the N-teminal of the polyprotein. The C-terminal part of the polyprotein contains sequence motifs which is a typical and well-characterized picornavirus nonstructural proteins: an RNA helicase, a chymotrypsin-like 3C protease, and an RNA-dependent RNA polymerase. Genetic analysis shows that the CSBV-LN had a 13-amino-acid deletion at amino acid positions 710–719 and 727–729 in comparison with CSBV-GZ and SBV-UK, and the SBV-UK had a 7-amino-acid deletion at amino acid positions 2124–2132 in comparison with CSBV-GZ and CSBV-LN, and the CSBV-GZ and CSBV-LN had a 6-amino-acid deletion at amino acid positions 2143–2150 in comparison with SBV-UK. Phylogenetic analysis using RdRp of selected picorna-like viruses shows that CSBV/SBV and Deformed Wing Virus (DWV) tend to group together, which possesses an RNA of similar size and gene order.

Conversion of VPg into VPgpUpUOH before and during Poliovirus Negative-Strand RNA Synthesis

ABSTRACT There are two protein primers involved in picornavirus RNA replication, VPg, the viral protein of the genome, and VPgpUpUOH. A cis-acting replication element (CRE) within the open reading frame of poliovirus (PV) RNA allows the viral RNA-dependent RNA polymerase 3DPol to catalyze the conversion of VPg into VPgpUpUOH. In this study, we used preinitiation RNA replication complexes (PIRCs) to determine when CRE-dependent VPg uridylylation occurs relative to the sequential synthesis of negative- and positive-strand RNA. Guanidine HCl (2 mM), a reversible inhibitor of PV 2CATPase, prevented CRE-dependent VPgpUpUOH synthesis and the initiation of negative-strand RNA synthesis. VPgpUpUOH and nascent negative-strand RNA molecules were synthesized coincident in time following the removal of guanidine, consistent with PV RNA functioning simultaneously as a template for CRE-dependent VPgpUpUOH synthesis and negative-strand RNA synthesis. The amounts of [32P]UMP incorporated into VPgpUpUOH and negative-strand RNA products indicated that 100 to 400 VPgpUpUOH molecules were made coincident in time with each negative-strand RNA. 3′-dCTP inhibited the elongation of nascent negative-strand RNAs without affecting CRE-dependent VPg uridylylation. A 3′ nontranslated region mutation which inhibited negative-strand RNA synthesis did not inhibit CRE-dependent VPg uridylylation. Together, the data implicate 2CATPase in the mechanisms whereby PV RNA functions as a template for reiterative CRE-dependent VPg uridylylation before and during negative-strand RNA synthesis.

Role of RNA Structures in Genome Terminal Sequences of the Hepatitis C Virus for Replication and Assembly

ABSTRACT Hepatitis C virus (HCV) is a positive-strand RNA virus replicating its genome via a negative-strand [(−)] intermediate. Little is known about replication signals residing in the 3′ end of HCV (−) RNA. Recent studies identified seven stem-loop structures (SL-I′, -IIz′, -IIy′, -IIIa′, -IIIb′, -IIIcdef′, and -IV′) in this region. In the present study, we mapped the minimal region required for RNA replication to SL-I′ and -IIz′, functionally confirmed the SL-IIz′ structure, and identified SL-IIIa′ to -IV′ as auxiliary replication elements. In addition, we show that the 5′ nontranslated region of the genome most likely does not contain cis-acting RNA structures required for RNA packaging into infectious virions.