MBT510/GEN551 Berg

Paper for 27 Nov 2001

Hartwell, L. 1980. Mutants of Saccharomyces cerevisiae unresponsive to cell division control by polypeptide mating hormone. J. Cell Biol. 85: 811-822.

Questions for Thought

As you read this paper, write down questions you have about the logic or rationale for each experiment, the method employed, and the conclusions drawn. Come up with at least five questions, more is better. (I came up with >20 questions!)

As you read, think about the questions listed below. Try to derive an answer from the paper or by thinking logically about the process. Focus on Tables I and X. We will discuss these questions and your questions in class. It may help to draw a flow chart of the various experiments.

At the beginning of class, turn in your questions along with BRIEF answers (one or two sentences) to the questions below that are typed in bold.

1) What was known at that time? What was the purpose of these experiments?

2) How did he make the mutants? Why test for mating ability at two temperatures? How many alleles of each gene? Are these genes the only ones required for mating? How do you know?

3) Complementation Tests:

a) Work through method of creating MATa strains from starting MATa strains. What is result for ste2? How could this gene be acting in the pheromone pathway?

b) Work through complementation tests (Fig. 1) and results in Table 1. Cryptopleurine causes loss of CRY+ chromosome and diploidization of cry- chromosome. He used the selection for cry sensitivity to obtain MATa/MATa diploids that would try to mate (diploids usually do not mate). He would then have diploids with which to test complementation of the ste mutations.

4) Table II: Why retest all the mutants for sterility? Why test different strains? What is he actually scoring? What is the phenotype? Why does some mating still occur?

5) Intrinsic v Extrinsic effects. Why do mixing experiments? What are possible outcomes? How would those be interpreted? Table III: What is evidence that defect is “cell autonomous”?

6) Morphology, agglutination, mating factor production/destruction, budding: What is the purpose of examining all these characteristics?

7) Tables VIII, IX, Suppression by cdc28: What is the logic of the experiments with cdc28? What is the result and what does that tell you about the function of these genes in the pheromone pathway? in cell cycle control?