Figure 1. LeuRS, as a sensor of AA, transmits a signal to TORC1.
A. In both yeast and mammalian cells, leucine loaded LeuRS, which is required for protein synthesis, binds and activates Gtr/Rag GTPases, which in turn activate TORC1. Activated TORC1 then facilitates protein synthesis, while turning off the protein recycling process, autophagy. B. A comparison between TORC1 activation in yeast and in mammalian cells. In yeast LeuRS was shown to bind and preserve GTP-bound Gtr1, while in mammalian cells LeuRS was shown to bind RagD and to act as a GAP that preserves the GDP-bound RagD. It is not known whether, through close proximity, the yeast LueRS acts as GAP for Gtr2 or the mammalian LeuRS protects the GTP-bound RagB (see text for details).
