Figure 5

Structural model for the binding of bHLH transcription factors to DNA. (A) Since 1 turn of double helix DNA is approximately 34 Å and requires 10.4 nucleotides, 1 EE-element, which consists of 12 nucleotides, spans 39.2 Å (34/10.4 × 12). (B) Two binding faces form a 55.8-degree angle (360/10.4 × 12–360). (C) The maximum dimension of the bHLH structure, which lies along the DNA, is about 32 Å, which is within the 39 Å calculated above and allows the binding. Green indicates a hetero complex of transcription factors such as BMAL1 and CLOCK; and light blue, unknown factors.