Main structural elements of Gα subunit and its interaction sites with its partners. Ribbon representation of transducin (Gαt) is shown in the centre as a prototypical example of Gα subunits. Ras-like GTPase and helical domains are shown as pale yellow and white, respectively. Three switch regions, indicated as S-I to S-III are colored green. Bound-nucleotide (GTPγS) is shown as cyan sticks in the centre of the molecule. The nomenclature for secondary structure is also indicated on the picture. The long N-terminal helix (26 residues) is missing in the structure. Pictures on the sides are surface representation of the molecule with the same orientation as the ribbon representation. Contact sites with Gβγ , RGS9 and phospodiesterase (PDEγ) , and sites involved in receptor recognition and interaction [1, 41, 42] are shown with different colors as indicated in the picture. All the pictures were rendered by using PyMol (DeLano Scientific LLC, South San Francisco, California, USA) with the deposited coordinates in Protein Data Bank (PDB code 1TAG-chainA).