The unique sequence of the herpes simplex virus 1 L component contains an additional translated open reading frame designated UL49.5.

We present evidence for the existence of an additional herpes simplex virus 1 gene designated UL49.5. The sequence, located between genes UL49 and UL50, predicts a hydrophobic protein with 91 amino acids. Attempts to delete UL49.5 were not successful. To demonstrate that UL49.5 is expressed, we made two recombinant viruses. First, we inserted in frame an oligonucleotide encoding a 15-amino-acid epitope known to react with a monoclonal antibody. This gene, consisting of the authentic promoter and chimeric coding domain, was inserted into the thymidine kinase gene of wild-type virus and in infected cells expressed a protein which reacted with the monoclonal antibody. The second recombinant virus contained a 5' UL49.5-thymidine kinase fusion gene. The protein expressed by this virus confirmed that the first methionine codon of UL49.5 served as the initiating codon. The predicted amino acid sequence of UL49.5 is consistent with the known properties of NC-7, a small capsid protein whose gene has not been previously mapped. A homolog of UL49.5 is present in the genome of varicella-zoster virus, located between homologs of UL49 and UL50.