In vitro Transcription of the Thymidine Kinase Gene of Herpes Simplex Virus

We transcribed in vitro a cloned 3.5-kilobase fragment of herpes simplex virus type 1 DNA that contains the gene for the viral thymidine kinase. Extracts from uninfected HeLa cells produced five in vitro transcripts, one of which initiated at the in vivo start site for the thymidine kinase mRNA (an early viral message). A second in vitro transcript initiated at or near the start site for a major late in vivo viral mRNA. The remaining three in vitro transcripts may correspond to minor in vivo mRNA species. Sequences similar to the ``T-A-T-A'' and ``C-A-A-T'' boxes, which may be involved in the control of transcription of a variety of viral and cellular genes, were found to precede the initiation site of each of the five in vitro transcripts. Considerable overlap of transcription units was observed.