Editorial Volume 10, Issue 5 pp 857—858

TORC1, stress and the nucleolus

Figure 1. Hypothetical model of TORC1 mediated control on several processes affecting the rDNA structure. A metaphase arrest in yeast yields a characteristic rDNA loop (green knobs). TORC1 stimulates transcription of rDNA. Although TORC1 complex is mainly located at the vacuole/lysosome (purple rectangle), pools could also exist in the nucleus (N) including at the rDNA. Stimulated TORC1 would impinge on the rDNA structure, while blocking sirtuins and Nem1/Spo7-Pah1 complex. Upon rapamycin treatment or calorie restriction, or by means of stresses like Heat Stress (HS), the rDNA shrinks into a compacted structure (not shown). TORC1 inhibition would lead to an increasing activity of sirtuins, and the Nuclear/Endoplasmic reticulum (ER) membrane would shrink as well, by altering Nem1-mediated lipid deposition. This latter effect would be apparently restricted to the rDNA/nucleolar region. The kinked lines with arrows would indicate compaction of the rDNA under TORC1 inhibition. White arrows within black boxes indicate specific actions on the rDNA.