RING1 IS ASSOCIATED WITH THE POLYCOMB GROUP PROTEIN COMPLEX AND ACTS AS A TRANSCRIPTIONAL REPRESSOR

The Polycomb (Pc) protein is a component of a multimeric, chromatin-as sociated Polycomb group (PcG) protein complex, which is involved in st able repression of gene activity, The identities of components of the PcG protein complex are largely unknown. In a two-hybrid screen with a vertebrate Pc homolog as a target, we identify the human RING1 protei n as interacting with Pc. RING1 is a protein that contains the RING fi nger motif, a specific zinc-binding domain, which is found in many reg ulatory proteins, So far, the function of the RING1 protein has remain ed enigmatic. Here, we show that RING1 coimmunoprecipitates with a hum an Pc homolog, the vertebrate PcG protein BMI1, and HPH1, a human homo log of the PcG protein Polyhomeotic (Ph), Also, RING1 colocalizes with these vertebrate PcG proteins in nuclear domains of SW480 human color ectal adenocarcinoma and Saos-2 human osteosarcoma cells, Finally, we show that RING1, like Pc, is able to repress gene activity when target ed to a reporter gene, Our findings indicate that RING1 is associated with the human PcG protein complex and that RING1, like PcG proteins, can act as a transcriptional repressor.