Roberts, R. L. and G. R. Fink. 1994. Elements of a single MAP kinase cascade in Saccharomyces cerevisiae mediate two developmental programs in the same cell type: mating and invasive growth. Genes Dev. 8: 2974-2985.

Questions for Thought

1) Summarize the basic observation concerning invasive and filamentous growth described in this paper. Why was the observation surprising?

2) The authors examine filamentous growth, bud site selection and agar penetration in haploid cells. The BUD genes and a subset of STE pathway genes regulate these processes in diploid cells.

How do the authors know the cells they are examining are haploid, not diploid?

How does BUD gene function compare in haploid and diploid cells? What are the BUD genes doing?

Which STE genes are acting in these processes? Which are not? Of those that do act during invasive growth, what aspects of the process are they regulating?

3) What is the evidence that FUS3 and KSS1 kinases act antagonistically in this pathway? Why do the authors invoke an additional, novel MAPK to explain these interactions? Do you agree? What other interpretations are possible? How would you test your hypotheses?

4) In Figure 8, the authors compare STE gene pathway functions in mating vs. invasive growth. What biological events or signals might be involved in inducing haploid cell invasive and filamentous growth? How would you identify them?

5) Flesh out this model by adding in regulatory points for bud site selection, agar penetration and filament formation. What are the functions of STE pathway genes in this process? What aspects are they regulating? How are the other behaviors regulated? Where do the BUD genes fit in?

6) The authors emphasize the point that the same MAPK cascade that induces G1 arrest and mating also regulates invasive cell growth. Propose three different mechanisms to explain how a kinase cascade might effect different biological consequences in a single cell type.