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Journal of Virology, July 2005, p. 8065-8078, Vol. 79, No. 13
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.13.8065-8078.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Gene 5 of the Avian Coronavirus Infectious Bronchitis Virus Is Not Essential for Replication

Rosa Casais, Marc Davies, David Cavanagh, and Paul Britton^*

Division of Molecular Biology, Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire, RG20 7NN, United Kingdom

Received 22 December 2004/ Accepted 16 March 2005

The avian coronavirus Infectious bronchitis virus (IBV), like other coronaviruses, expresses several small nonstructural (ns) proteins in addition to those from gene 1 (replicase) and the structural proteins. These coronavirus ns genes differ both in number and in amino acid similarity between the coronavirus groups but show some concordance within a group or subgroup. The functions and requirements of the small ns gene products remain to be elucidated. With the advent of reverse genetics for coronaviruses, the first steps in elucidating their role can be investigated. We have used our reverse genetics system for IBV (R. Casais, V. Thiel, S. G. Siddell, D. Cavanagh, and P. Britton, J. Virol. 75:12359-12369, 2001) to investigate the requirement of IBV gene 5 for replication in vivo, in ovo, and ex vivo. We produced a series of recombinant viruses, with an isogenic background, in which complete expression of gene 5 products was prevented by the inactivation of gene 5 following scrambling of the transcription-associated sequence, thereby preventing the expression of IBV subgenomic mRNA 5, or scrambling either separately or together of the translation initiation codons for the two gene 5 products. As all of the recombinant viruses replicated very similarly to the wild-type virus, Beau-R, we conclude that the IBV gene 5 products are not essential for IBV replication per se and that they are accessory proteins.

Present address: Laboratorio de Sanidad Animal, SERIDA, Travesía del Hospital 96, Jove del Medio, 33299 Gijón-Asturias, Spain.

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