The herpes simplex virus origins of DNA synthesis in the S component are each contained in a transcribed open reading frame.

In the herpes simplex virus 1 genome, the origins of viral DNA synthesis are located in the unique sequences of the L component (Oril) and in the reiterated sequences of the S component (OriS) located between the 5' terminus of the alpha 4 gene and the 5' terminus of either the alpha 22 (left terminus of the S component) or the alpha 47 (right terminus of the S component) gene. Studies prompted by the finding that only one, but not both, OriS sequence is dispensable for growth in cell culture indicate that each OriS sequence is contained in an open reading frame designated as OriSORF. The transcription of OriSORF is initiated approximately 860 nucleotides upstream from that of the alpha 4 gene and 162 nucleotides downstream, but on the opposite strand from the transcription initiation site of the alpha 22 or alpha 47 genes within the inverted repeat c sequence. The OriSORF transcript is 3' coterminal with the mRNA of the alpha 4 gene, polyadenylated but not spliced, transported into the cytoplasm, and capable of directing the synthesis of a 330-amino-acid protein with a translated molecular weight of approximately 34,000. Transcription is cycloheximide but not phosphonoacetate sensitive and is therefore regulated as either a beta or a gamma 1 gene. The implications of the transcription of OriS and of possible functions of the product of OriSORF are discussed.