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. 2008 Feb 27;3(2):e1663. doi: 10.1371/journal.pone.0001663

Figure 1. Integrative network of cAMP-PKA, MAPK and TOR pathways involved in the regulation of filamentous growth in Saccharomyces cerevisiae.

Figure 1

Mep2 functions in the upstream of cAMP and MAPK pathways as an ammonium sensor. Kelch repeat protein Gpb1/2 antagonizes Gpa2 and PKA of cAMP pathway and stabilizes Ira1, which inactivates Ras2 of MAPK pathway. In cAMP-PKA pathway, Ras2 and Gpa2 activate adenylate cyclase, Cyr1 to synthesis cAMP, which binds to PKA and relieves the inhibition of catalytic subunits Tpk1, Tpk2 and Tpk3. Tpk2 activates the transcriptional activator Flo8 involved in the regulation of FLO11. In MAPK pathway, Ras2 and Sho1 activates Cdc42-Ste20 complex, which in turn activates the MAPK cascade Ste11, Ste7 and Kss1 to control the transcriptional activator Ste12-Tec1. Nitrogen starvation or rapamycin treatment is shown to inactivate TOR pathway. Tor kinase phosphorylates Tap42, which complexes with phosphatase Sit4 and Pph21/22. Further, Sit4 and Pph21/22 controls Gln3 mediated NCR genes and Msn2/4 mediated STRE genes, respectively. Tor-activated Tap42 also participate in the global translational initiation. TOR pathway exerts translational control over G1 cyclin Cln3, which in turn controls the synthesis of other G1 cyclin Cln1/2 through transcriptional activator SBF. Cln1/2 is destabilized by Grr1 and is involved in the transcriptional activation of FLO11.