The terminal a sequence of the herpes simplex virus genome contains the promoter of a gene located in the repeat sequences of the L component.

The herpes simplex virus DNA genome consists of two covalently linked components, L and S. The unique sequences of the L component are flanked by 9-kilobase-pair inverted repeat sequences ab and b'a', whereas those of the S component are flanked by 6.5-kilobase-pair inverted repeat sequences c'a' and ca. We report that the 500-base-pair a sequence contains the promoter-regulatory domain and the transcription initiation site of a diploid gene, the coding sequences of which are located in the b sequences of the inverted repeats of the L component. The chimeric gene constructed by fusion of the a sequence to the coding sequences of the thymidine kinase gene and recombined into the viral genome was regulated as a gamma 1 gene. The size of the protein predicted from its sequence is 358 amino acids; it was designated as infected cell protein (ICP) 34.5. Thus, the inverted repeats flanking the unique sequences of the L component contain two genes specifying ICP0 and ICP34.5, respectively. Moreover, in addition to the cis-acting sites for the inversion of L and S components relative to each other, for cleavage of unit length DNA molecules from head-to-tail concatemers, and for packaging of the DNA into capsids, the a sequence also contains the promoter-regulatory domain and transcription initiation sites of a gene.