Now, Lee Bardwell and colleagues of the University of California, Irvine, CA, report that Kss1 is activated during mating, although the period of activation is shorter than for Fus3. This limitation on Kss1 is dependent not only on the presence of Fus3 but also (contrary to previous results) on Fus3 activity. The relevant target of Fus3 has not yet been determined.
“The idea that the specificity involves transient versus sustained activation of MAP kinase opens up a whole series of parallels with mammalian systems,” says Bardwell. In rat neurons, for example, transient MAP kinase activation downstream of EGF results in proliferation, whereas sustained activation downstream of NGF results in differentiation.The method by which sustained activation is decoded is unknown. One possibility is that a kinase must be active for long enough both to induce transcription and to phosphorylate the product of that transcription. ▪