vlf-1 Deletion Brought AcMNPV to Defect in Nucleocapsid Formation

State Key Laboratory for Biocontrol, School of Life Sciences, SunYat-Sen (Zhongshan) University, Guangzhou, People's Republic of China.
Virus Genes (Impact Factor: 1.58). 01/2006; 31(3):275-84. DOI: 10.1007/s11262-005-3242-3
Source: PubMed


Recent studies have provided direct evidence that the baculovirus very late factor 1 (VLF-I) of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) was essential for BV production. To elucidate how vlf-1 deletion blocks BV production we generated a vlf-1 knockout bacmid by ET-recombination technology on AcMNPV bacmid propagated in Escherichia coli. Bacmid DNA transfection and supernatant passage assay revealed that the vlf-1 knockout bacmid was unable to replicate in cell culture, while vlf-1 repair bacmid, which was generated by transposition of the vlf-1 ORF under control of its native promoter into polyhedrin gene locus of vlf-1 knockout bacmid, resumed viral replication ability at wildtype levels. Results of these assays proved the correct construction of the vlf-1 knockout bacmid. Subsequent electron microscopy revealed that the vlf-1 knockout bacmid failed to form nueleocapsid in the nuclei of the transfected cells. Instead, intensely electron-dense virogenic stroma characteristic of viral DNA synthesis were observed. Thus, it is demonstrated for the first time that vlf-1 knockout blocked nucleocapsid formation and the defective nucleocapsid formation resulted in the abolishment of BV and ODV production. Possible roles of vlf-1 in genome processing are suggested and discussed.

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    • "No upregulation of these transcripts was observed in male pupae (data not shown). Among the baculovirus core gene products playing a role in nucleocapsid packaging and assembly (Li et al., 2005; Wu et al., 2006; Slack & Arif, 2007; Braunagel & Summers, 2007) the following nudivirus-like proteins were identified in CiBV: 38K, VLF-1 and VP91; in addition a 19 kDa protein of unknown function was found (Table 1; Bézier et al., 2009a). The qRT-PCR measurements (Fig. 3a) revealed that upregulation was highest for 38K mRNA (approx. "
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    • "It was initially described as a factor involved in transcription of baculovirus very late genes. More recently it was shown to constitute a structural component of nucleocapsids and to play an important role in capsid assembly (Li et al., 2005; Vanarsdall et al., 2004, 2006). In mutant lacking the tyrosine of the recombination catalytic site, the nucleocapsids remain trapped in the nucleus suggesting that VLF-1 is involved in the final stage of the packaging process. "
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