Characterization of mutants of herpes simplex viruses, types 1 and 2, that produce fragments of the thymidine kinase polypeptide.

Seven tk- mutants of herpes simplex virus, type 2 (HSV-2), and three tk- mutants of herpes simplex virus, type 1 (HSV-1), were isolated which did not produce the thymidine kinase (TK) polypeptides but formed smaller polypeptides not seen in wild-type infected cells. Positive TK mRNA selection by hybridization to the cloned tk genes followed by in vitro translation identified the TK polypeptides. Comparisons of the products of partial proteolysis of the polypeptides of four HSV-2 and two HSV-1 tk- mutants to those of the parental TK polypeptides indicated that, in each case, the novel polypeptide was a fragment of the TK polypeptide, showing that these mutants have defects in the structural gene for tk. HSV-2 mutants of this sort have not been previously described. They and the HSV-1 mutants are similar to HSV-1 mutants reported previously. In addition, it was found that TK mRNA was present early in infection but was absent late in infection, suggesting that the shutoff of TK synthesis is due to message degradation. Also, HSV-2 TK mRNA did not hybridize to the cloned HSV-1 tk gene indicating that these genes have extensively diverged.