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J Virol. 1974 November; 14(5): 1199-1208
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Expression of the Viral Thymidine Kinase Gene in Herpes Simplex Virus-Transformed L Cells

¹ Department of Medical Viral Oncology, Roswell Park Memorial Institute, Buffalo, New York 14203

ABSTRACT

In these studies, the expression of thymidine kinase (TK) in normal and herpes simplex virus (HSV)-transformed L cells has been compared. In asynchronously dividing cultures of L cells, the TK activity rose and declined rapidly and coordinately with DNA synthesis. When net cell increase stopped, TK activity was at a minimum. In contrast, TK activity of HSV-transformed cells remained at a minimum during rapid DNA synthesis and gradually increased as the rate of DNA synthesis decreased. When net cell increase stopped, TK activity was at a maximum. In synchronous cultures of L cells, TK activity rose and fell coordinately with the rate of DNA synthesis. In synchronous cultures of HSV-transformed cells, no increase in TK activity was observed during the period of rapid DNA synthesis, i.e., the S phase. These findings indicated that the viral TK gene in HSV-transformed cells was not placed under the control of the cellular mechanisms which normally modulate the host cell TK gene. Lytic infection of HSV-transformed cells with a TK^– mutant of HSV-1 induced a four-to fivefold increase in viral TK. The TK of HSV-1 was induced in the HSV-1-transformed cells and HSV-2 in the HSV-2-transformed cells by this TK^– mutant. The same infection of normal L cells decreased the cellular TK activity by 80%. This stimulation, rather than inhibition, suggest that the viral gene in HSV-transformed cells retain some of its original viral characteristics.