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Updated: May 22, 2026

Functional Imaging of Viral Transcription Factories Using 3D Fluorescence Microscopy
Published on: January 18, 2018
Processivity factor of KSHV contains a nuclear localization signal and binding domains for transporting viral DNA
Yali Chen1, Mihai Ciustea, Robert P Ricciardi
1Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, 19104, USA.
Abstract:
Kaposi's sarcoma-associated human herpesvirus (KSHV) encodes a processivity factor (PF-8, ORF59) that forms homodimers and binds to viral DNA polymerase (Pol-8, ORF9). PF-8 is essential for stabilizing Pol-8 on template DNA so that Pol-8 can incorporate nucleotides continuously. Here, the intracellular interaction of these two viral proteins was examined by confocal immunofluorescence microscopy. When individually expressed, PF-8 was observed exclusively in the nucleus, whereas Pol-8 was found only in the cytoplasm. However, when co-expressed, Pol-8 was co-translocated with PF-8 into the nucleus. Mutational analysis revealed that PF-8 contains a nuclear localization signal (NLS) as well as domains located at the N-terminus and the C-proximal regions that are required for Pol-8 binding. This study suggests that the mechanism that enables PF-8 to transport Pol-8 into the nucleus is the first critical step required for Pol-8 and PF-8 to function processively in KSHV DNA synthesis.
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