VP64

VP64 is a transcriptional activation domain used in molecular biology to recruit transcriptional machinery and boost expression of target genes. It is composed of four tandem repeats of the activation domain from the herpes simplex virus protein VP16, creating a potent activator when fused to a DNA-binding moiety.

In practice, VP64 is commonly fused to DNA-binding proteins such as catalytically inactive Cas9 (dCas9) or transcription factors to form CRISPR activation (CRISPRa) tools. By guiding the fusion protein to a gene promoter, researchers can elevate transcription from that locus without altering the DNA sequence.

VP64 originated as part of the VP16 activation domain's use in gene expression studies; the tetramerized form is named VP64 to indicate its increased strength relative to single VP16 domains.

Variants: To achieve higher activation, combinations such as VPR (VP64-p65-Rta) have been developed, layering multiple activation domains to recruit transcriptional machinery more efficiently.

Limitations: Activation strength is context-dependent and varies with cell type, promoter environment, and chromatin state. Overactivation or unintended targets can occur, and delivery of large fusion proteins can pose technical challenges.

VP64 is widely used in research on gene regulation, synthetic biology, and CRISPR-based gene activation techniques.