FIG. 4.

A model for active repression by Runx1. In DN and ISP thymocytes, the interaction between Runx1 and P-TEFb brings the enhancer (E) into the close proximity of the silencer (S) and prevents P-TEFb from activating RNAPII, which is arrested at the promoter (P), thus actively repressing transcription elongation. In DP and CD4 SP thymocytes, the lack of Runx1 binding to the CD4 silencer frees P-TEFb to interact with RNAPII and to activate transcription elongation. Only RNAPII on the CD4 promoter is depicted in the model.