SUMMARYThe herpes simplex virus type 1 (HSV-1) polypeptide Vmw65 is a structural component of the virus particle and is also responsible for trans-induction of immediate early (IE) transcription. Functional domains of this polypeptide were investigated by constructing a series of 10 plasmids each with a 12 bp insertion in the gene encoding Vmw65. Plasmids were analysed for their ability to stimulate IE transcription in short term transfection assays, and the altered Vmw65 polypeptides were assayed for the ability to form an IE-specific protein-DNA complex (IEC) in vitro. A direct correlation was observed between stimulation of transcription and formation of IEC, strongly suggesting that IEC is an important intermediate in transcription activation. Plasmids were also tested for their ability to rescue the temperature-sensitive mutation in the HSV-2 assembly mutant ts2203, since marker rescue analysis indicated that this mutation maps within the gene encoding Vmw65. Five plasmids failed to rescue ts2203, thereby defining regions of Vmw65 required for virus assembly. The results show that distinct domains exist in Vmw65 for activation of transcription and assembly of virus.
In previous studies, the herpes simplex virus type 1 (HSV-1) mutant, in1814, which lacks the transinducing function of Vmw65, did not replicate in the trigeminal ganglia of mice following corneal inoculation but did establish a reactivatable latent infection in the ganglia 12 to 24 h after ocular infection. Since in1814 did not replicate in vivo, the molecular events during the establishment phase of latent HSV-1 infection could be characterized without the complications of concurrent productive viral infection. In comparison to parental HSV-1 strain 17 ÷, the expression of viral immediate early (IE), early and late genes and the levels of viral DNA in the trigeminal ganglia of mice following in1814 infection were greatly reduced.However, accumulation of latency-associated transcripts, a prominent feature of latent HSV-1 infection, occurred in a wild-type fashion. Furthermore, low levels of viral gene expression and an increase in the level of viral DNA in the inl814-infected ganglia were not detected until I to 2 days after the establishment of HSV-1 latency. Thus, IE gene expression and replication of viral DNA in the trigeminal ganglia are not prerequisites for the establishment of HSV-1 latency. These results suggest that the pathways leading to productive and latent infections in neurons may diverge at an early stage of the host-HSV-1 interaction and that the level of viral IE gene expression has a key role in determining the outcome of infection.
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