YAP1 (yes-associated protein 1), also known as YAP or YAP65, is a protein that acts as a transcriptional regulator by activating the transcription of genes involved in cell proliferation and suppressing apoptotic genes. YAP1 is inhibited in the Hippo signaling pathway which allows the cellular control of organ size and tumor suppression. YAP1 was first identified by virtue of its ability to associate with the SH3 domain of Yes and Src protein tyrosine kinases. YAP1 is a potent oncogene, which is amplified in various human cancers.