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Figure 8. Stained cells revealing the earliest stage of cell fusion during mating with two unbudded, Gl cells undergoing cell fusion (A) followed by nuclear fusion (B). Reprinted from ref 13 with permission.

Mating and cell division. Wolfgang Duntze and Tom Maney had discovered the presence of a mating pheromone made by Mat αcells and Duntze had found that it inhibited DNA synthesis of Mat α cells. We collaborated with them to analyze the cell cycle response to mating pheromone and found that it arrested cells at the CDC28 step. Over the next few years, we investigated the relationship between the mating pathway and the division pathway. I found that when asynchronous cultures of Mata and Mat αcells were mixed, they arrested one another in G1, and at the time of cell fusion, both cells were at the G1 stage. John Pringle and Linda Wilkenson found evidence for a Mata pheromone that arrested Mat αcells at the CDC28 step. These experiments demonstrated that cell division was integrated with cell mating because both haploid cell types produced pheromones that arrested the other cell at the beginning of the cell cycle.