YY1 AND C-MYC ASSOCIATE IN-VIVO IN A MANNER THAT DEPENDS ON C-MYC LEVELS

The c-Myc oncoprotein has previously been shown to associate with tran scription regulator YY1 and to inhibit its activity. We show herein th at endogenous c-Myc and YY1 associate in vivo and that changes in c-My c levels, which accompany mitogenic stimulation or differentiation of cultured cells, affect the ratio of free to c-Myc-associated YY1. We h ave also investigated the mechanism by which association with c-Myc in hibits Wi's ability to regulate transcription, c-Myc does not block bi nding of YY1 to DNA. However, protein association studies suggest that c-Myc interferes with the ability of YY1 to contact basal transcripti on proteins TATA-binding protein and TFIIB.