Figure 1.

Hes1 gene expression oscillation is regulated by negative feedback and instability of gene products. Activation of the Hes1 promoter (red) induces synthesis of both Hes1 mRNA (orange) and protein (blue). Hes1 protein then binds to N box sequences of the Hes1 promoter and represses its own expression (purple). This repression leads to disappearance of Hes1 mRNA and Hes1 protein because they are extremely unstable. Hes1 protein is degraded by the proteasome (green). Disappearance of Hes1 protein relieves negative autoregulation, allowing the next round of expression. As a result, Hes1 expression oscillates in individual cells (inlet). The periodicity of Hes1 oscillation is about 2 h in fibroblast cells and about 3–5 h in ES cells.