FIGURE 9.

A model for the dependence of the Gdu1D phenotype on LOG2 ubiquitin ligase activity. In the presence of LOG2 (yellow), GDU1 (green) overexpression activates an amino acid transport system either by directly associating with an amino acid exporter (red), by functioning through as yet-undiscovered facilitator(s) (X), or by down-regulating an inhibitor of the transporter. This process depends in part on GDU1-activated LOG2 ubiquitination activity. GDU1 may also be an adaptor protein that aids in the recognition of amino acid exporters or unknown inhibitors/facilitators. P. M., plasma membrane.