Heterologous expression and subcellular localization of pumpkin seed tonoplast intrinsic proteins (TIP) in yeast cells.

Two tonoplast intrinsic proteins (TIP) of pumpkin seeds, pMP23 and MP28, were expressed in yeast cells under control of the GAL1 promoter, and the subcellular localization of the proteins was analyzed. The pMP23 and MP28 stably accumulated in the yeast vacuolar membrane when the proteins were expressed in the proteinase A-deficient strain (pep4), which lacks the activities of vacuolar proteases. However, pMP23 and MP28 did not accumulate in the wild-type strain; the expressed pMP23 and MP28 were degraded in a proteinase A-dependent manner. These results indicate that pMP23 and MP28 are transported to the vacuolar membrane when expressed in yeast.