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. Author manuscript; available in PMC: 2013 Sep 15.
Published in final edited form as: Curr Opin Immunol. 2012 Mar 2;24(2):139–145. doi: 10.1016/j.coi.2012.02.002

Figure 2. Cd4 cis-regulatory elements.

Figure 2

Schematic representation (not on scale) of the Cd4 locus, with exons 1 and 2 (black boxes), the silencer (red-filled oval) and positive regulatory elements (green-filled rectangles), including the proximal enhancer (E4P), promoter (Pr) and a downstream enhancer known as ‘thymic enhancer’ (E4T) even though it is now known to be active in LTi cells, not in thymocytes. Transcription factors important for the activity of each element are indicated, as are cell subsets in which each element is active, or determines ‘epigenetic memory’ despite having no intrinsic activity in the subset. Note that while AP4 does not bind the silencer, it interacts with Runx molecules and could therefore ‘bridge’ that element with E4P. Factors distinct from Runx proteins are thought to contribute to Cd4 silencing because the silencer contains functionally important motifs in addition to Runx binding sites [21].