The proteolytic processing of a non-structural polyprotein segment from the cytoplasmic domain of NS2A to the C terminus of NS5 of Murray Valley encephalitis (MVE) virus was examined, when expressed from cDNA via a vaccinia virus recombinant, in transiently transfected COS cells, or synthesized by cell-free translation. Cleavages mediated by the virus-encoded proteinase domain in NS3 at the junctions of NS2A-2B, NS2B-3 and NS4B-5 were catalysed efficiently. However, the cleavage at the NS3-4A junction, also mediated by the NS3 proteinase, was greatly delayed. Little or no NS3 was found, but an 85K precursor molecule accumulated; this was identified as NS3-4A. Termination codons were introduced by site-directed mutagenesis at the junctions of the NS3-4A, NS4A-4B and NS4B-5 genes to generate C-terminal truncations of the MVE virus polyprotein segment. In expression studies of these constructs the predicted NS3-mediated proteolytic cleavages were catalysed, except for that at the NS3-4A junction. In co-infections and co-transfections with constructs encoding the MVE virus non-structural polyprotein region truncated at the C termini of NS3 or NS4A, efficient processing at the NS3-4A site was induced. Thus it appears that the MVE virus polyprotein is cleaved inefficiently in cis at the NS3-4A junction, whereas the site is processed efficiently in trans by mature NS3. The NS3-4A precursor is also seen in flavivirus-infected cells. Its function remains to be determined, but it could play a role in the replication of flavivirus, in view of the importance of polyprotein processing in the regulation of gene expression of positive-stranded RNA viruses, the modulation of processing at the NS3-4A site by NS3 or NS3-containing precursors described in the present study and the importance of NS3 as an integral part of the viral polymerase complex.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error