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Journal of Virology, May 2006, p. 4623-4632, Vol. 80, No. 9
0022-538X/06/$08.00+0     doi:10.1128/JVI.80.9.4623-4632.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Regulated Cleavages at the West Nile Virus NS4A-2K-NS4B Junctions Play a Major Role in Rearranging Cytoplasmic Membranes and Golgi Trafficking of the NS4A Protein

Jojanneke Roosendaal,2,{dagger} Edwin G. Westaway,2 Alexander Khromykh,1,2 and Jason M. Mackenzie1,2*

School of Molecular and Microbial Sciences, University of Queensland, St. Lucia, Brisbane, Queensland 4072,1 Sir Albert Sakzewski Virus Research Centre, Royal Children's Hospital, Herston, Brisbane, Queensland 4029, Australia2

Received 2 December 2005/ Accepted 9 February 2006

A common feature associated with the replication of most RNA viruses is the formation of a unique membrane environment encapsulating the viral replication complex. For their part, flaviviruses are no exception, whereupon infection causes a dramatic rearrangement and induction of unique membrane structures within the cytoplasm of infected cells. These virus-induced membranes, termed paracrystalline arrays, convoluted membranes, and vesicle packets, all appear to have specific functions during replication and are derived from different organelles within the host cell. The aim of this study was to identify which protein(s) specified by the Australian strain of West Nile virus, Kunjin virus (KUNV), are responsible for the dramatic membrane alterations observed during infection. Thus, we have shown using immunolabeling of ultrathin cryosections of transfected cells that expression of the KUNV polyprotein intermediates NS4A-4B and NS2B-3-4A, as well as that of individual NS4A proteins with and without the C-terminal transmembrane domain 2K, resulted in different degrees of rearrangement of cytoplasmic membranes. The formation of the membrane structures characteristic for virus infection required coexpression of an NS4A-NS4B cassette with the viral protease NS2B-3pro which was shown to be essential for the release of the individual NS4A and NS4B proteins. Individual expression of NS4A protein retaining the C-terminal transmembrane domain 2K resulted in the induction of membrane rearrangements most resembling virus-induced structures, while removal of the 2K domain led to a less profound membrane rearrangement but resulted in the redistribution of the NS4A protein to the Golgi apparatus. The results show that cleavage of the KUNV polyprotein NS4A-4B by the viral protease is the key initiation event in the induction of membrane rearrangement and that the NS4A protein intermediate containing the uncleaved C-terminal transmembrane domain plays an essential role in these membrane rearrangements.

* Corresponding author. Mailing address: School of Molecular and Microbial Sciences, University of Queensland, Coopers Road, St. Lucia, Brisbane, Queensland 4072, Australia. Phone: 617 3365 3302. Fax: 617 3365 4620. E-mail: j.mackenzie{at}uq.edu.au.

{dagger} Present address: Wageningen University and Research Centre, Molecular Genetics, Botanisch Centrum, Aboretumlaan 4, 6703 BD Wageningen, The Netherlands.

Journal of Virology, May 2006, p. 4623-4632, Vol. 80, No. 9
0022-538X/06/$08.00+0     doi:10.1128/JVI.80.9.4623-4632.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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