Molecular characterization of naturally occurring glycoprotein C-negative herpes simplex virus type 1.

We previously isolated glycoprotein C (gC)-negative herpes simplex virus type 1 (HSV-1) mutants, TN-1, TN-2 and TN-3, from a patient with recurrent herpetic keratitis at one-year intervals. In the present study, the molecular basis for the inability of these clinical isolates to express gC was examined. The nucleotide sequence of the gC gene of the TN-1 strain was compared with that of the HSV-1 KOS strain. In the open reading frame of the gC gene, there were 12 nucleotide differences between the TN-1 and KOS strains, seven of which led to amino acid substitutions. Importantly, one of them was the codon change from CAG for glutamine at position 280 to TAG for the amber termination codon. Accordingly, the TN-1 strain produced a truncated gC with a predicted molecular weight, which was secreted into the extracellular fluid. These results suggest that this amber mutation in the TN-gC gene results in a premature termination of gC translation and is the cause of the gC-negative phenotype of the TN strains. It is expected that these extremely rare HSV-1 strains will provide us with valuable information concerning the in vivo functions of gC, especially in ocular diseases.