VP16 is a part of the tegument of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) particles, and is a prototypical acidic activator. GAL4-VP16 is constructed by the fusion of the acidic activation domain of the HSV (herpes simplex virus) VP16 transactivator to the DNA binding domain of GAL4. VP16 (411-490) is the 89-residue activation domain of VP16 protein.
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The GAL4 protein of yeast activates the transcription of several genes involved in galactose metabolism. This event requires that GAL4 bind to upstream activation sites with the consensus sequence 5′-CGGN5(T/A)N5CCG-3′ . A fragment of the GAL4 protein, comprising amino acids 1-147, binds DNA but fails to activate transcription. Herpes virus VP16 activates expression of immediate early genes in virally-infected cells. As most other eukaryotic transcriptional activator proteins, VP16 has a modular domain structure: it′s N-terminus is involved in DNA-protein interactions, while its C-terminal 79 amino acids have proven to be an especially potent transactivation domain. When fused to the DNA-binding domain of the yeast GAL4, this VP16 fragment functions as an activator of transcription in yeast, mammalian cells and in vitro transcription assays. VP16 has been shown to bind to TBP, TFIIB, and replication factor A.
The GAL4 yeast protein is responsible for the induction of various genes involved in galactose metabolism. This requires the binding of GAL4 gene to the upstream activation sites containing the consensus sequence 5′-CGGN5(T/A)N5CCG-3′. VP16 protein is essential for inducing the expression of viral immediate-early (IE) genes. A fragment of the GAL4 protein, comprising amino acids 1-147, binds DNA but fails to activate transcription. The highly acidic C-terminal tail of VP16 functions as a potent transcriptional activator in mammalian cells. GAL4-VP16 construct functions as an activator which promotes transcription in mammalian cells.