Figure 7.

Repression by PU.1 can be caused by redistribution of a limiting co-regulator (co-regulator theft). Schematic depicts the complementary changes in factor binding patterns as well as in transcriptional activity of genes that are normally PU.1-dependent (right) or PU.1-inhibited (left), across the developmental stages when PU.1 goes from high to low (top) and then in an experimental condition when PU.1 is re-introduced into committed cells that have already turned off endogenous PU.1 (bottom). The figure shows that the redistribution of partner factors Runx1 (R) and Satb1 (S) by recruitment to PU.1 (P) binding sites occurs at the expense of sites that these factors would otherwise occupy together with other T-cell factors (T). Broken-line arrows (lower left) indicate that redistribution probably involves the dynamic equilibrium of binding of these factors between genomic sites that are differentially preferred in the presence and absence of PU.1. In at least some cases, the “theft” of the cofactors also results in relative closing of the chromatin at sites from which these cofactors are removed. Schematic modified from Hosokawa et al. (80).