7.06_2004_PS3 - 7.06 Spring 2004 PS 3 1 of 4 Problem Set 3...

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7.06 Spring 2004 PS 3 1 of 4 Problem Set 3 2004 1) You are a geneticist investigating the signal transduction pathway that allows yeast cells to sense and respond to mating factors. It has been known for some time that mating type a cells secrete a factor while mating type alpha cells secrete alpha factor. Mating type a cells respond to alpha factor by forming a mating projection known as a “shmoo.” Conversely, mating type alpha cells respond to a factor by also forming a shmoo. Assembly of the shmoo structure allows yeast cells of opposite mating type to find one another and enhances fusion of two haploid cells. This structure can be easily visualized by a conventional light microscope. a. How would you isolate mutants that are unable to sense or respond to the mating factor? b. How would you isolate genes responsible for the observed defect? c. Your competitors recently published a paper that defines the genetic network responsible for the yeasts’ mating response. Preliminary evidence suggests that the mating type factors bind to a G-protein coupled receptor that is linked to a signaling cascade that might resemble a MAP kinase-like pathway. The genes known to be involved are shm1, shm2, shm3, shm4 and shm5 (shm for shmoo). The authors failed to order these genes into a pathway. In order to salvage your scientific career, you perform some epistasis analysis to determine the order of function of these genes. Using a set of mutants in the mating response you produced the following data: i. A constitutively active shm4 mutant is unable to rescue the phenotype (no shmoo) of a shm3 deletion.
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7.06_2004_PS3 - 7.06 Spring 2004 PS 3 1 of 4 Problem Set 3...

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