Fig. 4: Changes in TORC1 activity upon amino acid supply disruption correlate with the law of demand.

A A schematic illustrating the activity outputs of the TORC1. Increased Sch9 phosphorylation and ribosome biogenesis are key readouts of TORC1 activation. TORC1 activity indicates the extent of amino acid demand in a given environment. B Assessment of TORC1 activity (based on Sch9 phosphorylation) after transiently disrupting (indicated) amino acid supply. Sch9 phosphorylation was assessed in the indicated amino acid dropouts (Arg, Pro, Lys), based on the electrophoretic mobility of Sch9 in extracts treated with NTCB. A representative blot (from n = 3, biological replicates) is shown. Comparisons are to -AA. C TORC1 activity as based on ribosomal transcript amounts, after transiently disrupting (indicated) amino acid supply. Relative changes in the expression of the indicated ribosomal subunit transcripts are shown. Comparisons are to +AA, n ≥ 4, biological replicates. Data for (4B and 4C) are displayed as mean ± SEM, ns denotes non-significant difference, ****p < 0.0001, Two-tailed student’s t-test. Data are provided in the Source Data file. D A four-quadrant chart to illustrate the relationship between the cost of biosynthesis/supply for an individual molecule of an amino acid, and the total demand for that amino acid. The size of the circles indicates (relative) intracellular concentrations of the respective amino acid. Based on this framework, amino acids with low supply costs and low demand will elicit a lower restoration response, and amino acids with low supply costs but high demand elicit the highest response. Distinct amino acids populate only three of the four quadrants, to complete the amino acid economy. There are no amino acids which have both high supply costs, as well as high demand in the cell.