Positive control of the herpes simplex virus thymidine kinase gene requires upstream DNA sequences.

We examined the ability of deleted versions of the herpes simplex virus type 1 thymidine kinase gene, present in biochemically transformed mouse cells, to be induced in trans to a higher level of expression by superinfecting herpes simplex virus immediate early gene products. The results demonstrate that sequences mapping between -200 and -80 and between -70 and -12 are required for induction. As these regions are largely coincident with the previously identified thymidine kinase gene promoter, the results suggest that herpes simplex virus immediate early gene products or their metabolic product activate thymidine kinase expression by acting at the promoter region to increase the rate of transcription.