Updated project metadata. To identify novel regulators of the Hippo pathway, we performed affinity purification-mass spectrometry (AP-MS) using Drosophila embryos overexpressing Yki-EGFP with a ubiquitous driver da-GAL4, as well as cultured S2 cells expressing Yki-SBP. We identified the core Hippo pathway components, multiple Hippo pathway regulators and functional groups, and several putative Yki interactors including Bonus (Bon). To identify additional cofactors that are recruited by Bon, we performed AP-MS using Bon-SBP expressed in Drosophila S2 cells. Further genetic tests revealed the involvement of Bon interactors, HDAC1, Su(var)2-10, and Hrb27C, in the Drosophila eye specification that is regulated by the Yki-Bon complex.