The protein ICP0 of herpes simplex virus type 1 is targeted to nucleoli of infected cells

This study describes the nucleolar localization of the viral protein ICP0 of herpes simplex virus type 1. We show that the RING finger domain of ICP0 is essential for ICP0 to localize in nucleoli of transfected and 4 hour-infected cells. ICP0 forms particular intranucleolar domains that do not correspond to any known nucleolar domains. This distribution was confirmed by immunoblots performed on fractionated infected cells. Quantitative RT-PCR experiments indicated that ICP0 did not increase the transcription from the RNA polymerase I (Pol I) promoter in transfected cells, an effect opposite to that observed on viral and cellular Pol II promoters. Nucleoli are thus, after PML bodies and centromeres, a novel nuclear structure targeted by ICP0.