Inhibition of potato virus Y NIa activity: preparation of monoclonal antibody directed against PVY NI protein that inhibits cleavage of PVY polyprotein

A partially purified nuclear inclusion (NI) fraction was obtained from toba cco plants infected by potato virus Y (PVY). Four monoclonal antibodies (MA bs) were produced and characterized using this semipurified fraction as ant igen. Data showed that only one was directed against NIa whereas two were d irected against cytoplasmic inclusion (CI) protein and the last one against coat protein (CP). These results were due to the fact that the semipurifie d NI fraction was usually contaminated with Cl and CP proteins. When used o n in situ immunofluorescence method the anti-NIa MAb showed accumulation of the NIa protein in both nucleus and cytoplasm. In vivo, this MAb was able to detect different forms of the NIa protein including precursors and cleav age products. It was also able to inhibit the cleavage of the polyprotein d etected in the semipurified NI.