Fig. 3. Ste5p conformational models. Two models for how the binding of Gß to Ste5p induces a conformational change in either (A) a folded dimer or (B) an anti-parallel dimer that is formed through interactions between the N- and C-terminal halves of Ste5p. The binding of the Gß dimer (Ste4p and Ste18p) is postulated to align the associated kinases so as to permit serial phosphoryation. The models are adapted from (Sette et al., 2000); see text for details. Note that serial phosphorylations would occur in cis in model A and in trans in model B.