YAP (Yes-associated protein, YAP65) was identified based on its ability to associate with the SH3 domain of Yes. It also binds to other SH3 domain-containing proteins such as Nck, Crk, Src, and Abl (1). In addition to the SH3 binding motif, YAP contains a PDZ interaction motif, a coiled-coil domain, and WW domains (2-4). While initial studies of YAP all pointed towards a role in anchoring and targeting to specific subcellular compartments, subsequent studies showed that YAP is a transcriptional coactivator by virtue of its WW domain interacting with the PY motif (PPxY) of the transcription factor PEBP2 and other transcription factors (5,6). In its capacity as a transcriptional coactivator, YAP is now widely recognized as a central mediator of the Hippo Pathway, which plays a fundamental and widely conserved role in regulating tissue growth and organ size. Upon phosphorylation at Ser127 by LATS1/2 kinases, YAP translocates to the cytoplasm, where it is sequestered through association with 14-3-3 proteins in an Akt-dependent manner (6-8).YAP (D8H1X) XP® Rabbit mAb recognizes endogenous levels of total YAP protein.