Schematic diagrams of the genome structure of the wild-type and recombinant HSV-1 viruses used in this study. Line 1, wild-type HSV-1 (YK304) genome carrying a bacmid (BAC) in the intergenic region between UL3 and UL4. Line 2, domain with the UL49A, UL50 (vdUTPase), and UL51 open reading frames. Line 3, recombinant virus YK751 with an S187A mutation in the UL50 (vdUTPase) gene. Line 4, recombinant virus YK752 with the repaired vdUTPase S187A mutation. Line 5, recombinant virus YK761 carrying the MEF foreign gene expression cassette (an MEF tag with Myc and Flag epitopes and a TEV protease cleavage site) inserted into the intergenic region between UL50 (vdUTPase) and UL51. Line 6, recombinant virus YK762 with the vdUTPase S187A mutation and carrying MEF. Line 7, recombinant virus YK764 with the vdUTPase S187A mutation and carrying the hDUT-N foreign gene expression cassette (the nuclear isoform of human dUTPase) inserted into the intergenic region between UL50 (vdUTPase) and UL51.