Figure 1. Diagram of the aerobically silenced, hypoxia-regulated promoter enhancer. A: Three copies of the neuron-restrictive silencer element (NRSE) and three copies of the hypoxia-regulated enhancer (HRE) were placed in alternating tandem order to form the hypoxia-regulated silenced element (HRSE), which is conditionally silenced during aerobic periods and robustly induced in hypoxia. This 3xHRSE domain is composed of the NRSE (S) and the HRH (H) tandemly repeated three times. This domain is ligated to a 6xHRE domain, which is six additional tandem repeats of the HRE. B: The table graphic represents the four pGL3-based firefly luciferase reporter plasmids constructed to test the relative activities of the hybrid and control promoters.