Fine-structure mapping and functional analysis of temperature-sensitive mutants in the gene encoding the herpes simplex virus type 1 immediate early protein VP175

Herpes simplex virus (HSV)-specific proteins fall into at least three kinetic classes whose synthesis is sequentially and coordinaely regulated. Temperature-sensitive (ts) mutants of one complementation group (1-2) are defective in the transition from immediate early to early and late protein synthesis. To elucidate the function of the 1-2 gene product in the HSV type 1 replicative cycle, nine ts mutants in this group were mapped by fine-structure analysis and characterized members of the group lie within the terminally repeated sequences of the S region of the genome. Fine-structure genetic and physical mapping permitted the mutations to be ordered within these sequences. Because it has been shown that the message for VP175 and the DNA template specifying this protein extend beyond the limits of the physical map of the mutations, it follows that the mutations must lie within the structural gene for VP175. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that most members of the group overproduced the immediate early proteins VP175, -136, -110, and -63 and markedly underproduced early and late proteins at the nonpermissive temperature. In temperature shiftup experiments, it was fund that the synthesis of early and late proteins ceased, whereas the synthesis of immediate early proteins began again. Thus, it is postulated that VP175 is (i) involved in the transition from immediate early to early protein synthesis, (ii) requird continuously to maintain early protein synthesis, (iii) autoregulated, acting to inhibit immediate early protein synthesis.