FIG. 1.

Schematic representation of HSV-1 tk gene and mutations in the seven-G homopolymer region. The top panel represents the tk gene, with the locations of the seven-G homopolymer region and the PCR primers shown. The bottom panel represents the wild-type TK protein and the mutated polypeptides predicted to correspond to mutations in the seven-G region. Gray boxes, ATP binding domains; striped boxes, nucleoside binding domains; bold lines, amino acid sequences resulting from frameshifts; aa, amino acids; dl, deletion; ins, insertion. The oval on the bottom polypeptide diagram indicates an insertion of one amino acid.