NUCLEAR IMPORT OF THE CAPSID PROTEIN OF TOMATO YELLOW LEAF CURL VIRUS(TYLCV) IN PLANT AND INSECT CELLS

The tomato yellow leaf curl virus (TYLCV) found in Israel is a whitefl y-transmitted monopartite geminivirus. Although geminiviruses have bee n found in the nuclei of phloem-associated cells, the mechanism of vir al invasion is poorly understood. The possible role of the TYLCV capsi d protein (CP), the only known component of the viral coat, in virus t ransport into the host cell nucleus was investigated by monitoring its specific nuclear accumulation in plant and insect cells. CP was fused to the P-glucuronidase (GUS) reporter enzyme to assay nuclear import in petunia protoplasts, and micro-injection of purified fluorescently labeled CP was used to examine its nuclear uptake in Drosophila embryo s. Both assays demonstrated that TYLCV CP is transported into plant-an d insect-cell nuclei by an active process of nuclear import via a nucl ear localization signal (NLS)-specific pathway. Using the GUS assay an d deletion analysis, the TYLCV CP NLS sequence was identified in the a mino-terminus of the protein.