Evidence for a relationship between equine abortion (herpes) virus deoxyribonucleic acid synthesis and the S phase of the KB cell mitotic cycle.

Autoradiographic analyses of deoxyribonucleic acid (DNA) synthesis in randomly growing KB cell cultures infected with equine abortion virus (EAV) suggested that viral DNA synthesis was initiated only at times that coincided with the entry of noninfected control cells into the S phase of the cell cycle. Synchronized cultures of KB cells were infected at different stages of the cell cycle, and rates of synthesis of cellular and viral DNA were measured. When cells were infected at different times within the S phase, viral DNA synthesis was initiated 2 to 3 hr after infection. However, when cells in G1 and G2 were infected, the initiation of viral DNA synthesis was delayed and occurred only at times corresponding to the S phase. The times when viral DNA synthesis began were independent of the time of infection and differed by as much as 5 hr, depending on the stage of the cell cycle at which cells were infected. Viral one-step growth curves were also related to the S phase in a manner which indicated a relationship between the initiation of viral DNA synthesis and the S phase. These data support the concept that initiation of EAV DNA synthesis is dependent upon some cellular function(s) which is related to the S phase of the cell cycle.