Loss of pseudorabies virus thymidine kinase activity due to a single base mutation and amino acid substitution

The nucleotide sequences of the coding region of the thymidine kinase (TK) gene of pseudorabies virus strain NIA3 and a TK^- mutant (ATK5) were determined. The coding region of the TK gene consists of 320 codons capable of producing a polypeptide with an M_r of 34979. The mutant expressed an inactive TK polypeptide when translated in vitro; a unique base substitution was detected in the mutant TK modifying amino acid position 13, at which aspartic acid replaces glycine. This modification affects the nucleotide-binding site, thus explaining the expression of an inactive TK polypeptide.