Fig. 11. Model for Ykt6 intramolecular interactions (left), targeting (middle) and activation upon membrane insertion (right). In this model, the Ykt6 longin domain (Lgn) interacts with the lipid groups (black) and the SNARE motif (red) such that the lipids are shielded from solvent and from premature insertion into membranes and the SNARE motif is sequestered and unavailable to other SNAREs. However, the longin domain is still available for interaction with a targeting component on the Ykt6 compartment. This allows inactive Ykt6 to be targeted to its specialized location, where binding between the targeting component and the longin domain results in: (1) interaction of the lipid group(s) with the membrane; (2) release of the longin domain from its interaction with the C-terminal lipid(s); and (3) release of the Ykt6 SNARE motif from sequestration to allow potential SNARE interactions.