Nuclear Import of the Capsid Protein of Tomato Yellow Leaf Curl Virus (TYLCV) in Plant Cells

Abstract

To investigate the possible role of tomato yellow leaf curl virus (TYLCV) coat protein (CP) in virus transport into the host cell nucleus, its accumulation in the nucleus was monitored. The interaction of the CP with the cytoplasm receptor karyopherin alpha and its ssDNA binding activity was also studied. A construct containing the TYLCV CP and the 3' end of the beta -glucuronidase (GUS) gene was introduced into petunia protoplasts. GUS activity was determined histochemically. The GUS-TYLCV CP fusion protein was specifically localized to the cell nucleus, suggesting that the TYLCV CP is a karyophilic protein containing a nuclear localization signal (NLS). Mutational analysis of the CP gene revealed that the first 38 amino acids were required for nuclear transport. The gene for karyopherin alpha from tomato was cloned and sequenced (accession number AF017252) and karyopherin alpha was shown to interact with TYLCV CP. Gel mobility shift assays were used to study the ssDNA-binding activity of the purified TYLCV CP. TYLCV CP had ssDNA binding activity and the activity was sequence non-specific, strong and cooperative