Fig. 3.

Ubiquitin serves as a signal to traffic GLUT4 into the endosomal system. Yeast containing (+) or lacking (−) active vacuolar proteases (RPY10 and SF838-9D) and producing various versions of GLUT4 [wild-type, non-ubiquitinated 7K/R, or an in-frame GLUT4-ubiquitin fusion protein (G4-Ub) as indicated: from pCAL4, pCAL5 or pRM24] were grown in media containing ammonium sulfate (Am) or proline (Pro) as sole nitrogen source. Lysates from these cells were immunoblotted for GLUT4 and Vti1 (loading control).