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J. Virol., 03 1997, 1946-1955, Vol 71, No. 3
RS Baric, B Yount, L Hensley, SA Peel and W Chen
Molecular mechanisms permitting the establishment and dissemination of a
virus within a newly adopted host species are poorly understood. Mouse
hepatitis virus (MHV) strains (MHV-A59, MHV-JHM, and MHV-A59/MHV- JHM) were
passaged in mixed cultures containing progressively increasing
concentrations of nonpermissive Syrian baby hamster kidney (BHK) cells and
decreasing concentrations of permissive murine DBT cells. From
MHV-A59/MHV-JHM mixed infection, variant viruses (MHV-H1 and MHV-H2) which
replicated efficiently in BHK cells were isolated. Under identical
treatment conditions, the parental MHV-A59 or MHV-JHM strains failed to
produce infectious virus or transcribe detectable levels of viral RNA or
protein. The MHV-H isolates were polytrophic, replicating efficiently in
normally nonpermissive Syrian hamster smooth muscle (DDT-1), Chinese
hamster ovary (CHO), human adenocarcinoma (HRT), primate kidney (Vero), and
murine 17Cl-1 cell lines. Little if any virus replication was detected in
feline kidney (CRFK) and porcine testicular (ST) cell lines. The variant
virus, MHV-H2, transcribed seven mRNAs equivalent in relative abundance and
size to those synthesized by the parental virus strains. MHV-H2 was an RNA
recombinant virus containing a crossover site in the S glycoprotein gene.
At the molecular level, episodic evolution and positive Darwinian natural
selection were apparent within the MHV-H2 S and HE glycoprotein genes.
These findings differ from the hypothesis that neutral changes are the
predominant feature of molecular evolution and argue that changing
ecologies actuate episodic evolution in the MHV spike glycoprotein genes
that govern interspecies transfer and spread into alternative hosts.
Copyright © 1997, American Society for Microbiology
Episodic evolution mediates interspecies transfer of a murine coronavirus
Department of Epidemiology, University of North Carolina at Chapel Hill, 27599-7400, USA.
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