PMC

Mechanism of ACV action.

Outline of in vivo experiments to determine properties of ACV^r viruses.

Loci of the ACV^r mutations discussed in the text. The top line represents the HSV tk gene and the vertical lines indicate the location of each homopolymeric sequence associated with resistance. Arrows denote the G-string and the C-chord. Below is shown the TK polypeptide, including the approximate location of the major functional sites in the protein.

Studies of the single base insertions in the G-string. Boxes represent TK polypeptides; wild type sequences are shown in gray and out-of-frame amino acids are shown by wavy lines. Nucleotide sequences and associated amino acids are shown. Estimated amounts of each polypeptide that are synthesized are shown on the right. A)Wild type tk. B) A single G insertion into the G-string. Full-length TK is generated via a net +1 ribosomal frameshift. C) A single base is inserted downstream of the G-string to simulate the requirement of a net +1 ribosomal frameshift for the synthesis of full-length TK, while maintaining the wild type length G-string.

Studies of ACV^r mutations associated with a homopolymeric sequence downstream of the G-string. Boxes represent TK polypeptides; wild type sequences are shown in gray and out-of-frame amino acids are shown by wavy lines. Nucleotide sequences and associated amino acids are shown. Estimated amounts of each polypeptide that are synthesized or genomes that are generated with specified sequences are shown on the right. A)Wild type tk. B) A net +1 ribosomal frameshift event appears to compensate for a deletion of a C in a homopolymeric sequence downstream of the G-string. Nine out-of-frame amino acids would be translated, which reduces the TK activity to 35%. Extrapolating, the TK-activity of this mutant is ∼0.9%.

Studies of two-base insertions in the G-string. Boxes represent TK polypeptides; wild type sequences are shown in gray and out-of-frame amino acids are shown by wavy lines. Nucleotide sequences and associated amino acids are shown. Estimated amounts of each polypeptide that are synthesized or genomes that are generated with specified sequences are shown on the right. A) Wild type tk. B) A double-G insertion into the G-string. Full-length TK is generated via a net -1 ribosomal frameshift. C) Reversion to the wild type phenotype occurs via the addition of a base into the 9 base G-string and is detected at a frequency of 3%. D) A single base is deleted downstream of the G-string to simulate the requirement of a net -1 ribosomal frameshift for the synthesis of full length TK, while maintaining the wild type length G-string.