Loss of thymidine kinase activity due to a base deletion in a candidate vaccine strain of bovine herpesvirus 2.

The nucleotide (nt) sequence of the thymidine kinase (TK) gene (a 918 nt long coding region) of two TK-deficient (TK) strains of bovine herpesvirus 2 (BHV-2) was determined. The candidate vaccine strain C290BU5, which was no longer able to cause disease, was found to have an A deletion after nt 887 of the TK gene with a predicted change of His 296 to Pro, altering the last 10 amino acids (aa) and extending the gene by another 34 aa. The strain which still caused disease, C290BU3, had a T insertion after nt 16 causing a predicted chain termination after only 16 aa.