A Herpes Simplex Virus Type 1 Mutant with a Deletion in the Polypeptide- coding Sequences of the ICP4 Gene

A deletion mutant derived from herpes simplex virus type 1 (HSV-1) strain ANG was analysed. The deletion mapped within the polypeptide-coding region of the immediate-early ICP4 gene. Based on DNA sequence data the deletion was shown to comprise 84 base pairs. In the wild-type genome of strain ANG these sequences were almost completely homologous to the known sequences of HSV-1 strain 17. The ICP4 polypeptide induced by the mutant was similar in size to the wild-type ICP4 protein and was recognized by a monoclonal antibody against ICP4. The data presented suggest that the deletion corresponds to a region on the ICP4 polypeptide that is non-essential for the replication of the virus in vitro. At least five immediate-early (IE) proteins can be identified during the infectious cycle of herpes implex virus type I (HSV-I; Honess & Roizman, 1974; Preston, 1979). The synthesis of these polypeptides i not dependent on the prior synthesis of other viral proteins. The IE polypeptide variously referred to as VP175 (Courtney & Benyesh-Melnick, 1974) or Vmw175 (Marsden et al., 1976) or ICP4 (Honess & Roizman, 1974) is the only IE gene product o which an essential function in replication has been assigned. Studies with temperature-sensitive mutants have shown that the ICP4 gene product is involved in the switch from immediate-early (ct) protein synthesis to the synthesis of early (fl) proteins and that it is required in a functiona