Thymidine Kinase Deletion Mutants of Herpes Simplex Virus Type 1

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Abstract
Deletions in the cloned thymidine kinase (TK) gene of herpes simplex virus type 1 (HSV-1), strain 17 syn+, were produced by 2 methods. Removal of a 506 base pair fragment from between the unique SstI and BglII restriction endonculease sites of pTK1 (HSV-1 BamHI p cloned in pAT153) and subsequent transformation of Escherichia coli resulted in the isolation of 50 deleted plasmids. Sequential digestion of pTK1 with BglII and nuclease BAL 31 followed by ligation and recleavage with BglII resulted in the isolation of 31 deleted plasmids. Three clones, pTK2, pTK3 and pTK4, obtained following BglII and SstI treatment of pTK1 were recombined with wild-type (wt) HSV-1 (17) syn+ DNA in baby hamster kidney (BHK) cells to produce TK- deletion mutants HSV-1 (17) TK 1301, HSV-1 (17) TK 1302 and HSV-1 (17) TK 1303, respectively. 5-Bromo-2''-deoxyuridine, 5-bromo-2''-deoxycytidine and 9-(2-hydroxyethoxymethyl)guanine were used to reduce the background of TK+ virus in heterogeneous recombinant stocks analyzed for the presence of TK- recombinants. All recombinant clones isolated produced a small syncytial plaque morphology in BHK cells. The mutants HSV-1 (17) TK 1301 and HSV-1 (17) TK 1302 were TK-, failed to producepolypeptides of MW 43,000 and 19,000 found in wt-infected cells and demonstrated 1-step growth curves different from wt virus and the TK- mutant HSV-1 (17) dPyk-7. Superinfection studies with HSV-1 (17) TK 1301, HSV-1 (17) TK 1302, HSV-1 (MDK) and HSV-1 (17) dPyk-7 indicated that all TK- mutants except dPyk-7 produce a trans-acting gene product which can switch on the transforming HSV-l TK gene.