Herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2) are doublestranded DNA 
viruses with a genome size of 152 kbp. The genome consists of two unique 
regions, U(L) (long) and U(s) (short), flanked by repeated sequences (Fig. 1; 
for review, see ref. 1). The two viruses are closely related, and both infect 
humans, producing mucocutaneous sores that are predominantly facial in the case 
of HSV-1 and genital in the case of HSV-2.