Figure 3.

Different modes of DNA looping in the Gal repressosome and transcription repression. Four possible arrangements of the GalR heterodimers on the operator sites are shown on the left. Each GalR dimer has two crescent-shaped tetramerization interfaces. Functional interfaces are colored green; the inactivated ones are red. GTGTAANC operator half sites are orange; GTGGTANC are light green. Arrows indicate the orientation of the operators. A V-shaped, stacked GalR tetramer (middle panel) forms upon interaction of the functional tetramerization interfaces (colored green on the left panel). The schematic DNA trajectory in each looping mode is shown in the middle panel. For detailed description of the antiparallel loops see Figure 6. Transcription of the gal promoters in different arrangements of GalR is shown on the right. Reactions contained 80 nM HU to allow repressosome formation. The transcript marked RNA1 served as an internal control (see text for details).