Mutant strains of herpes simplex deficient in thymidine kinase-inducing activity

Abstract

A mouse fibroblast subline [strain LM (TK −)] which lacks thymidine (TdR) and deoxyuridine (UdR) kinase activities acquires these enzymes following infection by herpes simplex virus. Mutant strains of herpes simplex have been isolated, which are resistant to bromodeoxyuridine (BUdR) and iododeoxyuridine (IUdR), and deficient in enzyme-inducing activity. The herpes simplex mutants fall into 3 groups: (1) mutant strains that induce either very low levels of TdR kinase activity or none at all; (2) mutant strains that induce approximately normal levels of TdR-H 3 uptake into the nuclei of 4–14% of the LM (TK −) cells; and (3) mutant strains that induce only very light TdR-H 3 labeling of the nuclei of 22–63% of the LM (TK −) cells. Three mutants from group I have been propagated for several passages in LM or in LM (TK −) cells in media lacking BUdR. LM (TK −) cells were then challenged with virus from each of the passages and tested for TdR-H 3 incorporating activity. The experiments demonstrated that these mutants do not undergo gross reversion. Infection with parental herpes simplex enhanced the TdR and UdR kinase activities of LM cells, while infection with herpes simplex mutants reduced these enzymatic activities. The uridine kinase activity of both LM and LM (TK −) cells was reduced following inoculation of cultures with either parental or mutant herpes simplex strains. Growth of parental herpes simplex in LM (TK −) cells was markedly inhibited by either 25 μg/ml BUdR or 25 μg/ml IUdR. Similarly growth of parental virus in LM cells was inhibited by 25 μg/ml BUdR. However, growth of mutant 2011 occurred in LM (TK −) cells in the presence of 500 μg/ml BUdR and was only partially inhibited in LM cells at a BUdR concentration of 200 μg/ml BUdR. Growth of mutant 2006 in LM (TK −) cells was not inhibited by 250 μg/ml IUdR.