Fig 1.

The MAPK and PKA pathways in filamentation. See the text for details. The precise molecular signaling mechanisms are not clear. In addition to the activation of the filamentous-growth MAPK and PKA pathways by Ras2, as shown here, it has been reported that these branches can be stimulated in a Ras2-independent manner, as well. Our data suggest that the loss of V-ATPase activity in vma mutants strongly stimulates both Ste20 and Tpk2, probably because these cells are unable to efficiently store and mobilize nutrients in vacuoles.