Fig 7.

Model depicting Rhb1-TOR signaling in the regulation of SAP2 expression. In the absence of Rhb1 (“1”) or in cells treated with rapamycin (“2”), TOR signaling directly or indirectly affects SAP2 expression by transmitting the signal from Gln3 and Gat1 to activate STP1 expression. The SPS complex processes Stp1, and the active form of Stp1 in turn triggers SAP2 expression. Sap2 is processed before secretion into the environment. Enriched extracellular amino acids from extracellular proteins digested by Sap2 or other protease may also transmit a signal to activate the Tor1 kinase (“3”) (which may or may not occur through the SPS sensor) to inhibit SAP2 expression (and thus the Sap2 protein level) and other SPS-responsive genes. CM, cell membrane; NM, nuclear membrane. An asterisk indicates the active form of a particular protein, and a dashed line represents a hypothetical correlation.