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J. Virol., Dec 1997, 9045-9053, Vol 71, No. 12
M Zafrullah, MH Ozdener, SK Panda and S Jameel
Hepatitis E virus (HEV) is a major human pathogen in the developing world.
In the absence of an in vitro culture system, very little information
exists on the basic biology of the virus. A small protein (approximately
13.5 kDa) of unknown function, pORF3, is encoded by the third open reading
frame of HEV. We expressed pORF3 in transiently transfected COS-1 and Huh-7
cells and showed that it is a phosphoprotein which is modified at a serine
residue(s). Deletion and site-directed mutants were created to establish
Ser-80 as the phosphorylation site. This residue is present within a
conserved primary sequence that showed consensus sites for phosphorylation
by p34cdc2 kinase (cdc2K) and mitogen-activated protein kinase (MAPK). In
vitro experiments with hexahistidine-tagged pORF3 expressed either in
Escherichia coli or in COS-1 cells showed efficient phosphorylation with
exogenously added MAPK. The pORF3 mutants also exhibited an in vitro
phosphorylation profile with MAPK which was identical to that observed in
vivo. In its primary sequence, pORF3 possesses two highly hydrophobic
N-terminal domains. On subcellular fractionation, pORF3 was found to
partition with the cytoskeletal fraction, and this association with the
cytoskeleton was lost on deletion of hydrophobic domain I (amino acid
residues 1 to 32). These results suggest that HEV pORF3 is a
cytoskeleton-associated phosphoprotein and are discussed in terms of a
possible function for pORF3 within the HEV replicative cycle.
Copyright © 1997, American Society for Microbiology
The ORF3 protein of hepatitis E virus is a phosphoprotein that associates with the cytoskeleton
Virology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India.
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