Yin Yang 1 Associated Factor 2 Interacts with the Yin Yang 1 REPO Domain

The Yin Yang 1 (YY1) REPO domain was found to be necessary and sufficient to recruit Polycomb proteins to DNA and silence a transgeneic reporter gene (PNAS 2006 103:19296‐19301). The objective in this study was to characterize the molecular mechanisms responsible for Polycomb recruitment by REPO. Yin Yang 1 Associated Factor 2 (Yaf2) was identified as a putative ligand for the REPO domain in a yeast two‐hybrid screen of a mouse 17 day embryonic cDNA library. Full length YY1 (1‐414) and the YY1 REPO domain (YY1 201‐226), but not the YY1 REPO deletion (YY1 1‐414del201‐226), were capable of interacting with Yaf2 in the two hybrid assay. These observations were validated in vivo using a chromatin immunoprecipitation assay. A transgenic Drosophila strain was prepared expressing flag‐tagged Yaf2 under control of the heat shock 70 promoter. This strain was crossed to a strain containing the transgenic reporter element (BGUZ) and either heat shock 70 driven‐Gal4 DNA binding domain (GALDBD) or the GALDBD fused to YY1 201‐226 (GALREPO). FlagYaf2 was immunoprecipitated at the BGUZ locus in the presence of GALREPO but not in the presence of GALDBD. Together, these results indicate that the YY1 REPO recruits Yaf2 to DNA and likely contributes to Polycomb‐mediated silencing. This work was funded by a faculty development grant awarded to F.W from Philadelphia University.