Nuclear targeting of the cauliflower mosaic virus coat protein

The entry of the viral genomic DNA of cauliflower mosaic virus into the nuc leus is a critical step of viral infection. We have shown by transient expr ession in plant protoplasts that the viral coat protein (CP), which is proc essed from the product of open reading frame IV, contains an N-terminal nuc lear localization signal (NLS). The NLS is exposed on the surface of the vi rion and is thus available for interaction with a putative NLS receptor. Ph osphorylation of the matured CP did not influence the nuclear localization of the protein but improved protein stability. Mutation of the NLS complete ly abolished viral infectivity, thus indicating its importance in the virus life cycle. The NLS seems to be regulated by the N terminus of the precaps id, which inhibits its nuclear targeting. This regulation could be importan t in allowing virus assembly in the cytoplasm.