Yeast Genetics and Molecular Biology 1998
College Park, Maryland
August 1998

Name: San-Segundo, Pedro A.
Mailing Address: HHMI, Yale University, 266 Whitney Ave, New Haven, CT 06520, USA
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Phone and Fax numbers: (203) 432 5052, (203) 432 3263


Pch2 provides a link between meiotic checkpoint control, silencing and the nucleolus.

Pedro A. San-Segundo , G. Shirleen Roeder
HHMI, Yale University, 266 Whitney Ave, New Haven, CT 06520, USA

During the meiotic cell cycle, a checkpoint prevents progression into meiosis I until recombination is completed, thus ensuring the proper segregation of chromosomes. The ZIP1 gene of S. cerevisiae encodes a component of the central region of the synaptonemal complex. In the zip1 mutant, chromosomes fail to synapse and undergo a reduced level of crossing over, resulting in cell cycle arrest at the pachytene stage of prophase I. PCH2 is a meiosis-specific gene identified in a genetic screen for checkpoint mutants that relieve the meiotic arrest of zip1 . Sporulation frequency, crossing over and spore viability are not significantly affected in the pch2 mutant. The zip1 pch2 double mutant displays the wild-type level of sporulation, but spore viability is decreased due to the absence of Zip1. Most of the Pch2 protein localizes to the unsynapsed nucleolar region (rDNA), and a small fraction is found in a punctate pattern along synapsed chromosomes overlapping with Zip1. Pch2 is required for the repression of meiotic recombination in the rDNA. The silencing factor Sir2 is also required for this repression. Localization of Pch2 to the nucleolus depends on Sir2, and sir2 also bypasses the meiotic arrest of zip1 . The recombination protein Hop1, which is excluded from the rDNA in wild type, is found in the nucleolus in the pch2 and sir2 mutants. Possible relationships between the nucleolus and meiotic checkpoint control will be discussed.

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