Accumulation of helper component/proteinase and coat protein of turnip mosaic virus in intact plants.

The helper component/proteinase (HC/Pro) protein of turnip mosaic virus (TuMV) was fused with glutathione S-transferase (GST) and expressed as a fusion protein in Escherichia coli. The quality of antiserum raised against the GST-HC/Pro fusion protein was compared to that of antiserum raised against coat protein (CP) by image analyser. The result showed that these antisera were of similar quality. Then the both antisera were used to follow the time course of accumulation of HC/Pro protein and CP in intact TuMV-infected leaves. CP appeared first at day 3 post inoculation (p.i.) and gradually accumulated in uninoculated upper leaves, whereas HC/Pro protein appeared first at day 4 p.i., accumulated up to day 7 p.i. and then gradually decreased. Potyvirus proteins are encoded by a single translation unit spanning most of the genome and are presumably synthesized in equimolar ratios. Therefore, the reduced accumulation of HC/Pro protein in relation to CP at one month p.i. in infected plants is presumed to be the result of its degradation.