Mutational dissection of the HSV-1 immediate-early protein Vmw175 involved in transcriptional transactivation and repression

Vmw 175 is one of five immediate-early (IE) proteins encoded by herpes simplex virus type-1 (HSV-1). It is required for the transcription of later classes of genes and for the accompanying repression of IE expression. Vmwl 75 has been shown to be a transectivator of transcription and also to autoregulate its own synthesis. We have made a large number of small, in-frame, insertion and deletion mutants of a plasmid-borne copy of the gene encoding Vmw175. Study of the activity of the resultant mutant polypeptides in transient transfection assays has defined the regions of the protein important for the repression of its own promoter, and for the transactivation of an HSV early promoter in synergy with another HSV IE protein, Vmwl 10. Large stretches of the protein are relatively unimportant for either function, while the regions most sensitive to disruption correlate to sequences conserved between Vmwl 75 and VZV 140K, the corresponding transactivating protein of Varicella-Zoster virus. The region from amino acids 275 to 490 is particularly important for both repression and transactivation, whereas that from around 840 to 1100 seems to be more important for transactivation than repression. The nuclear localization signal has been mapped to within residues 682–774