Functional dissection of VP16, the trans-activator of herpes simplex virus immediate early gene expression.

TLDR

Herpes simplex virus type 1 virions contain the 65‑kD VP16 protein, which activates transcription of the five immediate‑early genes via cis‑regulatory elements adjacent to each gene; VP16 activity can also be studied by cotransfecting cells with a VP16‑encoding plasmid and an IE promoter‑driven reporter. We used this assay to test mutant forms of VP16. We identified two VP16 domains essential for IE gene induction: a carboxy‑terminal acidic 78‑aa region and an amino‑terminal region that confers gene specificity, suggesting VP16 achieves specificity through protein–protein rather than protein–DNA interactions.

Abstract

Mature virions of herpes simplex virus type 1 contain an activating factor that primes transcription from the five virally encoded immediate early (IE) genes. This activator is specified by a 65-kD polypeptide termed VP16. The action of VP16 is mediated through cis-regulatory elements located in regions adjacent to each IE gene. Although VP16 is normally introduced into cells by infecting virions, its trans-activating function can also be observed by cotransfecting cells with a plasmid that encodes VP16 along with a reporter gene driven by IE cis-regulatory sequences. We have used such an assay to examine the function of mutant forms of VP16. Our results provide tentative identification of two domains of VP16 that are crucial to its role in the induction of IE gene expression. One domain is located within the carboxy-terminal 78 amino acids of VP16 and is characterized by its acidity. Another domain, located in a more amino-terminal region of the protein, appears to tailor the specificity of VP16 for IE genes. According to the results presented in this and the accompanying paper, we predict that VP16 achieves IE gene specificity via protein: protein, rather than protein: DNA, interaction.