Analysis of transcriptional regulatory signals of the HSV thymidine kinase gene: identification of an upstream control region.

We have identified a transcriptional control region of the herpes simplex virus tk gene. This finding results from in vivo transcription assays of specific deletion mutants constructed in vitro. A region located between 40 and 100 nucleotides upstream from the putative transcription start site of the tk gene can promote transcription by RNA polymerase form II in the complete absence of the mRNA-coding component of the gene. When the region is deleted enzymatically from a 5' direction, accurate transcriptional expression is reduced by a factor of 50. The small remaining level of accurate transcription is eliminated by deletion of sequences from 32 to 16 nucleotides upstream from the the structural gene. It appears that the sequences between 16 and 32 nucleotides upstream from the 5' terminus of the tk gene are required to specify the exact start site of transcription. Control of both the efficiency of transcription and rough specification of the position of initiation, however, depends on sequences 40--100 nucleotides upstream from the tk structural gene.