This peptide is amino acids 48 to 57 fragment of TAT with an additional cysteine residue at the N-terminus. This peptide contains the protein transduction domain (PTD) of the HIV Tat protein that inhibits HSV-1 entry. The addition of a cysteine residue to the N-terminus of the Tat-PTD (Tat-C peptide) improves the antiviral activity against HSV-1 and HSV-2. Tat-C acts extracellularly, blocking entry of adsorbed virus immediately without eluting virions.