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An improved reverse genetics system for generation of bovine viral diarrhea virus as a BAC cDNA.

ABSTRACT: Full length cDNA clones of bovine viral diarrhea virus (BVDV) with a low-copy number plasmid backbone have not proven to be stable when propagated in bacteria. To improve stability, pBAS, a bacterial artificial chromosome (BAC) plasmid was used to construct a full length cDNA clone of BVDV strain SD1, which has a genomic size of 12.3 kb. The resulting clone pBSD1 was propagated stably for at least 10 passages in three different Escherichia coli strains at two different incubation temperatures as determined by sequencing the progeny plasmids. In vitro transcripts derived from pBSD1 were homologous in size and had an infectious efficiency as high as approximately 5.0 x 10(5)FFU/microg RNA in MDBK cells. The recovered virus, BSD1, harbored the five artificially introduced silent point mutations as genetic markers and was similar to wild type SD1 in viral growth kinetics, RNA replication, and protein expression. This BAC clone provides a stable reverse genetics system for manipulation and study of BVDV genes.

SUBMITTER: Fan ZC

PROVIDER: S-EPMC7172198 | biostudies-literature | 2008 May

REPOSITORIES: biostudies-literature

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An improved reverse genetics system for generation of bovine viral diarrhea virus as a BAC cDNA.

Fan Zhen-Chuan ZC Bird R Curtis RC

Journal of virological methods 20080328 2

Full length cDNA clones of bovine viral diarrhea virus (BVDV) with a low-copy number plasmid backbone have not proven to be stable when propagated in bacteria. To improve stability, pBAS, a bacterial artificial chromosome (BAC) plasmid was used to construct a full length cDNA clone of BVDV strain SD1, which has a genomic size of 12.3 kb. The resulting clone pBSD1 was propagated stably for at least 10 passages in three different Escherichia coli strains at two different incubation temperatures as ...[more]

PMID: 18374992

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Project description:Historically part of the coronavirus (CoV) family, torovirus (ToV) was recently classified in the new family Tobaniviridae. While reverse genetics systems have been established for various CoVs, none exist for ToVs. Here, we developed a reverse genetics system using an infectious full-length cDNA clone of bovine ToV (BToV) in a bacterial artificial chromosome (BAC). Recombinant BToV harboring genetic markers had the same phenotype as wild-type (wt) BToV. To generate two types of recombinant virus, the hemagglutinin-esterase (HE) gene was edited, as cell-adapted wtBToV generally loses full-length HE (HEf), resulting in soluble HE (HEs). First, recombinant viruses with HEf and hemagglutinin (HA)-tagged HEf or HEs genes were rescued. These exhibited no significant differences in their effect on virus growth in HRT18 cells, suggesting that HE is not essential for viral replication in these cells. Thereafter, we generated a recombinant virus (rEGFP) wherein HE was replaced by the enhanced green fluorescent protein (EGFP) gene. rEGFP expressed EGFP in infected cells but showed significantly lower levels of viral growth than wtBToV. Moreover, rEGFP readily deleted the EGFP gene after one passage. Interestingly, rEGFP variants with two mutations (C1442F and I3562T) in nonstructural proteins (NSPs) that emerged during passage exhibited improved EGFP expression, EGFP gene retention, and viral replication. An rEGFP into which both mutations were introduced displayed a phenotype similar to that of these variants, suggesting that the mutations contributed to EGFP gene acceptance. The current findings provide new insights into BToV, and reverse genetics will help advance the current understanding of this neglected pathogen. IMPORTANCE ToVs are diarrhea-causing pathogens detected in various species, including humans. Through the development of a BAC-based BToV, we introduced the first reverse genetics system for Tobaniviridae. Utilizing this system, recombinant BToVs with a full-length HE gene were generated. Remarkably, although clinical BToVs generally lose the HE gene after a few passages, some recombinant viruses generated in the current study retained the HE gene for up to 20 passages while accumulating mutations in NSPs, which suggested that these mutations may be involved in HE gene retention. The EGFP gene of recombinant viruses was unstable, but rEGFP into which two NSP mutations were introduced exhibited improved EGFP expression, gene retention, and viral replication. These data suggested the existence of an NSP-based acceptance or retention mechanism for exogenous RNA or HE genes. Recombinant BToVs and reverse genetics are powerful tools for understanding fundamental viral processes, pathogenesis, and BToV vaccine development.

Project description:Unique to pestiviruses, the N-terminal protein encoded by the bovine viral diarrhea virus (BVDV) genome is a cysteine protease (Npro) responsible for a self-cleavage that releases the N terminus of the core protein (C). This unique protease is dispensable for viral replication, and its coding region can be replaced by a ubiquitin gene directly fused in frame to the core. To develop an antiviral assay that allows the assessment of anti-hepatitis C virus (HCV) NS3 protease inhibitors, a chimeric BVDV in which the coding region of Npro was replaced by that of an NS4A cofactor-tethered HCV NS3 protease domain was generated. This cofactor-tethered HCV protease domain was linked in frame to the core protein of BVDV through an HCV NS5A-NS5B junction site and mimicked the proteolytic function of Npro in the release of BVDV core for capsid assembly. A similar chimeric construct was built with an inactive HCV NS3 protease to serve as a control. Genomic RNA transcripts derived from both chimeric clones, P(H/B) (wild-type HCV NS3 protease) and P(H/B(S139A)) (mutant HCV NS3 protease) were then transfected into bovine cells (MDBK). Only the RNA transcripts from the P(H/B) clone yielded viable viruses, whereas the mutant clone, P(H/B(S139A)), failed to produce any signs of infection, suggesting that the unprocessed fusion protein rendered the BVDV core protein defective in capsid assembly. Like the wild-type BVDV (NADL), the chimeric virus was cytopathic and formed plaques on the cell monolayer. Sequence and biochemical analyses confirmed the identity of the chimeric virus and further revealed variant viruses due to growth adaptation. Growth analysis revealed comparable replication kinetics between the wild-type and the chimeric BVDVs. Finally, to assess the genetic stability of the chimeric virus, an Npro-null BVDV (BVDV-Npro in which the entire Npro coding region was deleted) was produced. Although cytopathic, BVDV-Npro was highly defective in viral replication and growth, a finding consistent with the observed stability of the chimeric virus after serial passages.

Dataset Information

An improved reverse genetics system for generation of bovine viral diarrhea virus as a BAC cDNA.

Publications

An improved reverse genetics system for generation of bovine viral diarrhea virus as a BAC cDNA.

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