Two newly detected nonstructural viral proteins in potyvirus-infected cells.

The existence of two viral RNA-encoded proteins in cells infected with tobacco vein mottling potyvirus (TVMV) has been demonstrated. One of the proteins (named 34K) maps at the N-terminus of the TVMV polyprotein and the other (42K) between the helper component and cylindrical inclusion proteins; both had previously been predicted in the consensus potyviral genetic map. The 34K and 42K coding regions of TVMV were cloned separately in a bacterial expression vector and the proteins were isolated from transformed Escherichia coli. These were used to raise polyclonal antibodies which reacted specifically with proteins of the expected size in immunoblots of extracts of TVMV-infected tobacco leaves and protoplasts. In addition to 42K, the anti-42K serum detected similar amounts of a second protein of apparent size 37 kDa that was absent in 42K-expressing bacteria. Both 34K and 42K were present predominantly in membrane-enriched fractions of extracts of TVMV-infected tobacco leaves. Computer analysis of the deduced amino acid sequence of 42K suggests that this viral protein may be an integral transmembrane protein.