The capsid protein of tomato yellow leaf curl virus binds cooperatively to single-stranded DNA

The capsid protein (CP) of tomato yellow leaf curl virus (TYLCV) is the only known component of the virus coat. Here, we identify TYLCV CP as a single-stranded (ss) DNA binding protein. Purified TYLCV CP bound ssDNA in a highly cooperative and sequence-nonspecific fashion. TYLCV CP-ssDNA complexes were resistant to nucleolytic digestion and remained stable at relatively high salt concentrations. Because TYLCV CP is known to contain an active nuclear targeting signal, we propose that its association with the viral genomic ssDNA mediates TYLCV entry into the host cell nucleus during the infection process.