JVI Accepts, published online ahead of print on 4 November 2009

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J. Virol. doi:10.1128/JVI.01548-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Early Gene hhi1 Reactivates Latent HzNV-1 Virus in the Latently Infected Cells

Yueh-Lung Wu, Carol-P Wu, Han Tang, Chi-Hua Chang, Hong-Hwa Chen, Song-Tay Lee^*, and Yu-Chan Chao^*

Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 105; Institute of Biotechnology, National Cheng Kung University, Tainan 701; Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei 105; Department of Chemistry, National Tsing Hua University, Hsinchu 300; Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, National Chung Hsing University and Academia Sinica, Nankang, Taipei 105; Department of Life Sciences, National Chung Hsing University, Taichung 400; Department of Biotechnology, Southern Taiwan University of Technology, Yung-Kang City, Tainan 710; Department of Biology, National Cheng Kung University, Tainan 701; Department of Plant Pathology and Microbiology, National Taiwan University, Taipei 106, Taiwan, ROC

^* To whom correspondence should be addressed. Email: songtlee{at}mail.stut.edu.tw. mbycchao{at}gate.sinica.edu.tw.

Heliothis zea nudivirus 1 (HzNV-1), previously known as Hz-1 virus, is an insect virus able to establish both productive and latent infections in several lepidopteran insect cells. Here, we have cloned and characterized one of the HzNV-1 early genes, hhi1, which maps to the HindIII-I fragment of the viral genome. During the productive viral infection, a 6.2-kb hhi1 transcript was detectable as early as 0.5 h post infection (hpi). The level of transcript reached a maximum at 2 hpi, and gradually decreased after 4 hpi. The transcript was not detectable during the latent phase of viral infection. Upon cycloheximide treatment, much higher levels of hhi1 transcript were detected throughout the productive viral infection cycle, suggesting that newly synthesized proteins are not needed for the expression of hhi1. Nevertheless, viral co-infection can further stimulate the expression of transfected hhi1 promoter in a plasmid. Transient hhi1 expression in latently-infected cells resulted in a significant increase in viral titer and viral DNA propagation, suggesting that hhi1 plays a critical role in viral reactivation. Additional experiments showed that 6 early genes, which possibly function in transcription or DNA replication, were activated in the latent cells upon hhi1 transfection. Among these six genes, orf90 and orf121 expressions could be induced by hhi1 alone without the need for other viral genes. Our discovery should be useful for future mechanistic study of the switches of latent/productive HzNV-1 viral infections.