FIGURE 12.

Schematic representation of the five methods used to down-regulate TorC1 along with the downstream nuclear Gln3-Myc¹³ localization outcomes they elicit and phosphatase requirements they possess. The five methods used to down-regulate TorC1 activity are listed in black at the top and are labeled 1–5, with their outcomes on Gln3-Myc¹³ localization below the abscissa. The shaded areas demarcate the hierarchal phosphatase requirements (indicated in pink below the perturbation used) for each of the experimental perturbations employed to elicit nuclear Gln3-Myc¹³ localization (green arrows). Horizontal black lines at high and lower nitrogen availability denote steady-state nitrogen levels for the nitrogen sources indicated below them. Red arrows indicate increases in amino acid levels when additional nitrogen sources are added to proline-grown cells or protein synthesis is inhibited. Both conditions lead to Gln3 being sequestered in the cytoplasm. Fine vertical dotted lines indicate the points at which nitrogen starvation was imposed, and the bold dotted line indicates the extension of the time course required for starvation of cells cultured in limiting (30 μgm/ml) leucine. The green dot denotes the point at which nitrogen starvation has proceeded to the point of triggering G₁ arrest of the cell cycle. At the time resolution of present experiments, it is not possible to determine whether Gln3-Myc¹³ begins entering the nucleus slightly prior to or concomitantly with the onset of cell cycle arrest. In sit4Δ cells, the two events appear to occur close together. It is clear, however, that G₁ arrest is not required for Gln3-Myc¹³ to relocate to the nucleus. Therefore, we conclude that it occurs just before or at the same time as cells begin arresting. Nitrogen availability is indicated on the ordinate, whereas the abscissa indicates increasing time expiring after a given treatment (addition of nitrogen or translation inhibitors) or starvation has commenced.