FIG. 6.

Schematic representation of the cellular roles of Btn1p and Btn2p. (A) Step 1 shows the deletion of btn1Δ. Step 2 shows that btn1Δ results in decreased arginine uptake into the vacuole (12). Step 3 shows that btn1Δ results in the up-regulation of Btn2p (23). Step 4 shows that btn1Δ results in the up-regulation of Hsp30p (11, 23). Step 5 shows that the up-regulation of Hsp30p down-regulates overactive Pma1p (23). Step 6 shows that the up-regulation of Hsp30p decreases excess proton pumping across the plasma membrane (23). (B) Step 1 shows that Btn2p interacts with Yif1p and is involved in correctly localizing this protein to the Golgi apparatus (3). Step 2 shows that Btn2p interacts with and is involved in correctly localizating Rhb1p (2). Step 3 shows that Rhb1p negatively regulates the Can1p permease, which transports arginine and lysine into the cell (27). Step 4 shows decreased uptake of arginine into the cell (2). Step 5 shows that Btn2p interacts with Ist2p, which shows homology to ion channel proteins and may be involved in the transport of an as-yet-unidentified cation across the plasma membrane.