The <i>Saccharomyces cerevisiae</i> Ssy5 signaling protease is a core component of the plasma membrane (PM)-localized SPS (Ssy1-Ptr3-Ssy5) sensor<i>.</i> In response to extracellular amino acids, the SPS-sensor orchestrates the proteasomal degradation of the inhibitory Ssy5 prodomain.
Evidence from multiple laboratories has implicated Ssy1, a nontransporting amino acid permease, as the receptor component of the yeast plasma membrane (PM)-localized SPS (Ssy1-Ptr3-Ssy5)-sensor.