YAP1 contains a WW domain that is found in various structural, regulatory and signaling molecules in yeast, nematode, and mammals, and may be involved in protein-protein interaction.

The human and mouse cDNAs encode deduced 493- and 531-amino acid proteins, respectively, with significant sequence similarity to the chicken protein. All 3 contain a putative protein module of 38 amino acids that is found in various structural, regulatory, and signaling molecules in yeast, nematode, and mammals and may be involved in protein-protein interaction. The mouse protein contains an imperfect repeat of the module. Because one of the prominent features of the sequence motif is 2 tryptophans, it has been designated the WW domain .