Mutational Analysis of the Herpes Simplex Virus Type 1 Trans-inducing Factor Vmw65

Medical Research Council Virology Unit, Church Street, Glasgow G11 5JR, U.K. The 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 ts 2203, since marker rescue analysis indicated that this mutation maps within the gene encoding Vmw65. Five plasmids failed to rescue ts 2203, 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. Keywords: HSV-1, trans -inducing factor, mutagenesis in vitro Present address: Department of Molecular Biology, Edinburgh University, King's Buildings, Mayfield Road, Edinburgh EH9 3JR, U.K. Received 5 April 1988; accepted 6 July 1988.