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Journal of Virology, October 2005, p. 12742-12751, Vol. 79, No. 20
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.20.12742-12751.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Virology Division, Department of Infectious diseases and Immunology, Faculty of Veterinary Medicine and Institute of Biomembranes, Utrecht University, 3584 CL Utrecht, The Netherlands
Received 6 April 2005/ Accepted 1 August 2005
Coronaviruses are enveloped, positive-stranded RNA viruses considered to be promising vectors for vaccine development, as (i) genes can be deleted, resulting in attenuated viruses; (ii) their tropism can be modified by manipulation of their spike protein; and (iii) heterologous genes can be expressed by simply inserting them with appropriate coronaviral transcription signals into the genome. For any live vector, genetic stability is an essential requirement. However, little is known about the genetic stability of recombinant coronaviruses expressing foreign genes. In this study, the Renilla and the firefly luciferase genes were systematically analyzed for their stability after insertion at various genomic positions in the group 1 coronavirus feline infectious peritonitis virus and in the group 2 coronavirus mouse hepatitis virus. It appeared that the two genes exhibit intrinsic differences, the Renilla gene consistently being maintained more stably than the firefly gene. This difference was not caused by genome size restrictions, by different effects of the encoded proteins, or by different consequences of the synthesis of the additional subgenomic mRNAs. The loss of expression of the firefly luciferase was found to result from various, often large deletions of the gene, probably due to RNA recombination. The extent of this process appeared to depend strongly on the coronaviral genomic background, the luciferase gene being much more stable in the feline than in the mouse coronavirus genome. It also depended significantly on the particular genomic location at which the gene was inserted. The data indicate that foreign sequences are more stably maintained when replacing nonessential coronaviral genes.
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