Figure 10.

Cys-20 is probably located at the dimer interface and near DNA in the class I TCP-DNA complex. A, Alignment of the HLH regions of class I TCP proteins and the bHLH proteins PHO4, USF, and MyoD. Positions a and d (boxed) are occupied by hydrophobic residues and are located at the dimer interface. Cys-20 is located at position d₁ (boxed in yellow) in class I TCP proteins. B, The structure of the PHO4 bHLH domain bound to DNA (Shimizu et al., 1997). Leu-16, located at position d₁ of helix I in both monomers, is shown in yellow. The right panel shows a detail of the region around Leu-16. Structures were visualized using Swiss-PdbViewer (http://www.expasy.org/spdbv/).