Plasma membrane regulator of high affinity polyamine and carnitine transport; has similarity to transporters but lacks transport activity; may act as a sensor that transduces environmental signals; has a positive or negative regulatory effect on transcription of many transporter genes; null mutant is cycloheximide (CHX) resistant; ubiquitinated Agp2p is rapidly degraded in a Brp1p-dependent manner in the presence of CHX; localizes to the plasma membrane, the vacuolar membrane and the ER membrane