YEAST MUTANTS THAT PRODUCE A NOVEL TYPE OF ASCUS CONTAINING ASCI INSTEAD OF SPORES

Tetraploid yeast cells lacking BFR1 or overexpressing an essential gen e BBP1 produce a novel type of ascus that contains asci instead of spo res. We show here that the asci within an ascus likely arise because a /alpha spores undergo a second round of meiosis. Cells depleted of Bbp 1p or lacking Bfr1p are defective in a number of processes such as nuc lear segregation, bud formation, cytokinesis and nuclear spindle forma tion. Furthermore, deletion of BFR1 or overexpression of BBP1 leads to an increase in cell ploidy, indicating that Bfr1p and Bbp1p play role s in both the mitotic cell cycle and meiosis. Bfr1p and Bbp1p interact with each other in a two hybrid assay, further suggesting that they m ight form a complex important for cell cycle coordination.