In yeast, Vps74p mediates the Golgi membrane retention of glycosyltransferases by incorporating these enzymes into coat protein complex I (COPI) coated vesicles. VPS74 is not an essential gene indicating that there must be a parallel pathway of VPS74 in the COPI mediated traffic from Golgi to ER or within Golgi apparatus. Dr. TU in our lab found a vps74 temperature sensitive mutant. In order to find which genes may function in the parallel pathway of Vps74p, I did a dosage suppressor screen of this vps74 temperature sensitive mutant and found many genes could suppress the temperature sensitive growth phenotype of this vps74 strain. These dosage suppressors didn’t affect the retrograde transport of Kre2p and Dcr2p from Golgi to ER. Only MAD1 among these suppressors could suppress...[ Read more ]

In yeast, Vps74p mediates the Golgi membrane retention of glycosyltransferases by incorporating these enzymes into coat protein complex I (COPI) coated vesicles. VPS74 is not an essential gene indicating that there must be a parallel pathway of VPS74 in the COPI mediated traffic from Golgi to ER or within Golgi apparatus. Dr. TU in our lab found a vps74 temperature sensitive mutant. In order to find which genes may function in the parallel pathway of Vps74p, I did a dosage suppressor screen of this vps74 temperature sensitive mutant and found many genes could suppress the temperature sensitive growth phenotype of this vps74 strain. These dosage suppressors didn’t affect the retrograde transport of Kre2p and Dcr2p from Golgi to ER. Only MAD1 among these suppressors could suppress the calcofluor white sensitivity of vps74 temperature sensitive mutant. In cells, there are two pools of Mad1p, one is associated with Mad2p, and another is free. From our experiments, free Mad1p may have a new role in protein traffic except for its function in spindle assembly checkpoint and may localize to Golgi through interaction with Coy1p. In the future, I will keep on investigating the reasons for the suppression of these dosage suppressors, and for Mad1p, I will make sure Mad1p really localize in Golgi and find its cargoes if function in protein traffic.