Human Cytomegalovirus Primase UL70 Specifically Interacts with Cellular Factor Snapin

Genomic DNA synthesis is a universally conserved process for all herpesviruses, including human cytomegalovirus (HCMV). HCMV UL70 is believed to encode the primase of the DNA replication machinery, a function which requires localization in the nucleus, the site of viral DNA synthesis. No host factors that interact with UL70 have been reported. In this study, we provide the first direct evidence that UL70 specifically interacts with Snapin, a human protein that is predominantly localized in the cytoplasm and is associated with cellular vesicles. The interaction between UL70 and Snapin was identified in both the two-hybrid screen in yeast and coimmunoprecipitation in human cells. The nuclear import of UL70 was decreased in cells overexpressing Snapin and increased in cells in which the expression of Snapin was downregulated with anti-Snapin small interfering RNA (siRNA) molecules, respectively. Furthermore, viral DNA synthesis and progeny production were decreased in cells overexpressing Snapin and increased in the anti-Snapin siRNA-treated cells, respectively. In contrast, no significant difference in the nuclear level of UL70, viral DNA synthesis, and progeny production was found among the parental cells and cells that either expressed a control empty vector or were treated with control siRNA molecules that did not recognize any viral or cellular transcripts. Our results suggest that Snapin may play a key role in regulating the cellular localization of UL70 in HCMV, leading to modulation of viral DNA synthesis and progeny production.