Fig. 4. Ste5p oligomerization/recruitment model. An alternative model, in which a Ste5p dimer forms higher-order oligomers by binding to Gß. In this scenario, a Ste5p dimer can exist with a protected RING-H2 domain as a folded dimer of parallel strands or dimer of anti-parallel strands (A) or as an open dimer of parallel strands in which the RING-H2 domain is accessible to homo-dimerize and bind Gß (B). Higher-order oligomers can form through N- to C-terminal interactions, the binding of Gß driving the formation of higher-order oligomers at the plasma membrane by interfering with intramolecular interactions. Two types of higher-order oligomer are shown: tandem head-to-tail oligomers and stacked anti-parallel oligomers. The higher-order oligomers could conceivably promote serial phosphorylation in trans.