Fig. 7. Regulation of growth by PAT-related transporters. Model illustrating the role of PAT-related transporters in Drosophila cell growth. Although general amino acid transporters (AAT) and PATs can potentially activate TOR by increasing bulk intracellular amino acid concentrations (grey arrows), PAT-related transporters (here labelled PAT) have unique growth regulatory properties that, at least in the case of PATH, involve a local sensing mechanism (red arrows from PATH and PAT), which is modulated by InR/Tsc/Rheb. Genetic data suggest that these transporters modulate TOR signalling, but they may also affect growth via a parallel pathway that appears to affect S6K activation. The TOR signalling pathway negatively feeds back to upstream InR signalling via a mechanism that is uncharacterised in Drosophila (red bracket).