Hererford, L. and Hartwell, L. 1974. Sequential gene function in the initiation of Saccharomyces cerevisiae DNA synthesis. J. Mol. Biol. 84: 445-461.

Questions for Thought

1) Summarize the state of knowledge at that time. What is the pathway they are studying? What are the possible choices a yeast cell might make at this stage of the cell cycle? What was the purpose of these experiments? What are the two general approaches that they take to achieve their purpose?

2) Table 1: Explain the logic of the reciprocal shift experiments. What are essential aspects of these experiments? What are "restrictive conditions"? What is meant by "terminal phenotype"?

3) Figure 1: Explain the result with cdc4. How do they know how long to leave the cells at 36^oC? What are they assaying? What if their only assay was cell division? What if the blocks to cell cycle advancement are slowly imposed?

Note: we will focus on Figure 1. Figures 2 and 3 give similar results.

4) Table 2: Explain the logic of the double mutant studies. What is an essential aspect of the mutant phenotypes for this experiment to work? What if they don’t have null alleles?

5) Table 3: Summarize their results. How do they put cdc4 before cdc7? What evidence corroborates their inferred gene order?

6) Summarize the logic of these methods and indicate the restrictions or caveats to each approach.