Human cytomegalovirus UL84 localizes to the cell nucleus via a nuclear localization signal and is a component of viral replication compartments.

The UL84 open reading frame encodes a protein that is required for origin-dependent DNA replication and interacts with the immediate-early protein IE2 in lytically infected cells. Transfection of UL84 expression constructs showed that UL84 localized to the nucleus of transfected cells in the absence of any other viral proteins and displayed a punctate speckled fluorescent staining pattern. Cotransfection of all the human cytomegalovirus replication proteins and oriLyt, along with pUL84-EGFP, showed that UL84 colocalized with UL44 (polymerase accessory protein) in replication compartments. Experiments using infected human fibroblasts demonstrated that UL84 also colocalized with UL44 and IE2 in viral replication compartments in infected cells. A nuclear localization signal was identified using plasmid constructs expressing truncation mutants of the UL84 protein in transient transfection assays. Transfection assays showed that UL84 failed to localize to the nucleus when 200 amino acids of the N terminus were deleted. Inspection of the UL84 amino acid sequence revealed a consensus putative nuclear localization signal between amino acids 160 and 171 (PEKKKEKQEKK) of the UL84 protein.