Integrins of the beta7 subfamily, alpha4 beta7 and alphaE beta7, contribute to lymphocyte homing and to the development of protective or autoreactive immune responses at mucosal sites. The beta subunits of integrins are considered important for regulation of stimulated cell adhesion and adhesion-dependent signal transduction. Using a yeast interaction trap screen, a human WD repeat protein, termed WAIT-1, was isolated that interacts with the integrin beta7 cytoplasmic tail and is homologous to mouse EED and Drosophila ESC proteins. WAIT-1 also binds to the cytoplasmic domains of alpha4 and alphaE but not to those of integrin beta1, beta2, and alphaL subunits. Association of WAIT-1 and beta7-integrin was confirmed by coprecipitation from transiently transfected 293 cells. The binding site for WAIT-1 was mapped to a short membrane-proximal region of the beta7 cytoplasmic tail with Tyr-735 being of critical importance. Northern blot analysis revealed multiple WAIT-1-related transcripts with differential expression in circulating leukocytes, tissue-resident cells of diverse origin, and lymphoid malignancies. These results suggest that WAIT-1, together with the recently identified RACK1, may define a novel subfamily of WD repeat proteins that interact with distinct subsets of integrin cytoplasmic tails and may act as specific regulators of integrin function.