TOR modulates GCN4-dependent expression of genes turned on by nitrogen limitation

In Saccharomyces cerevisiae, the rapamycin-sensitive TOR signaling pathway plays an essential role in up-regulating translation initiation and cell cy cle progression in response to nutrient availability. One of the mechanisms by which TOR regulates cell proliferation is by excluding the GLN3 transcr iptional activator from the nucleus and, in consequence, preventing its tra nscriptional activation therein. We examined the possibility that the TOR c ascade could also control the transcriptional activity of Gcn4p, which is k nown to respond to amino acid availability. The results presented in this p aper indicate that GCN4 plays a role in the rapamycin-sensitive signaling p athway, regulating the expression of genes involved in the utilization of p oor nitrogen sources, a previously unrecognized role for Gcn4p, and that th e TOR pathway controls GCN4 activity by regulating the translation of GCN4 mRNA. This constitutes an additional TOR-dependent mechanism which modulate s the action of transcriptional activators.