Subcellular localization of the US3 protein kinase of herpes simplex virus type 2

One supposes that herpes simplex virus US3 gene product possessing serine/threonine protein kinase activity is a cytoplasmic enzyme. To determine its subcellular localization during viral replication we prepared an antiserum to a synthetic oligopeptide corresponding to the N-terminal region of the US3 protein of HSV type 2 strain 186. The US3 protein first appeared in the cytoplasm of infected cell at 4 h postinfection but strong fluorescence was detected in the nuclei at 8 h postinfection. At 12 h postinfection fluorescence was mainly detected in the cytoplasm, again. Further, the US3 protein expressed alone was widely distributed throughout the cell, indicating that the US3 protein by itself can be localized in the nuclei even in the absence of any other vital proteins. These observations suggest that the HSV-2 US3 protein kinase may function not only in the cytoplasm but also in the nuclei.