A single major immediate-early virus gene product is synthesized in cells productively infected with herpesvirus saimiri.

A major virus-specific immediate-early (IE) polypeptide with an apparent mol. wt. of 52 000 (52K) was synthesized immediately after the removal of a cycloheximide block applied to owl monkey kidney cell cultures at the time of infection with high multiplicities of herpesvirus saimiri (HVS). The IE 52K polypeptide was phosphorylated and accumulated rapidly and efficiently in the nucleus of infected cells. Monoclonal antibodies to IE 52K and to a major non-structural delayed-early (DE) DNA-binding protein with similar electrophoretic mobility (DE 51K) were used to show that the IE 52K protein and DE 51K proteins are antigenically distinct. The monoclonal antibody to the IE 52K protein of HVS strain 11 reacted in immune precipitation and immunofluorescence tests with polypeptides of similar mol. wt. present as nuclear antigens in cells infected with heterologous strains of HVS and herpesvirus ateles.