Mutually dependent degradation of Ama1p and Cdc20p terminates APC/C ubiquitin ligase activity at the completion of meiot
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RESEARCH
Open Access
Mutually dependent degradation of Ama1p and Cdc20p terminates APC/C ubiquitin ligase activity at the completion of meiotic development in yeast Grace S Tan1,2,4, Rebecca Lewandowski2, Michael J Mallory3, Randy Strich2 and Katrina F Cooper2*
Abstract Background: The execution of meiotic nuclear divisions in S. cerevisiae is regulated by protein degradation mediated by the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase. The correct timing of APC/C activity is essential for normal chromosome segregation. During meiosis, the APC/C is activated by the association of either Cdc20p or the meiosis-specific factor Ama1p. Both Ama1p and Cdc20p are targeted for degradation as cells exit meiosis II with Cdc20p being destroyed by APC/CAma1. In this study we investigated how Ama1p is down regulated at the completion of meiosis. Findings: Here we show that Ama1p is a substrate of APC/CCdc20 but not APC/CCdh1 in meiotic cells. Cdc20p binds Ama1p in vivo and APC/CCdc20 ubiquitylates Ama1p in vitro. Ama1p ubiquitylation requires one of two degradation motifs, a D-box and a “KEN-box” like motif called GxEN. Finally, Ama1p degradation does not require its association with the APC/C via its conserved APC/C binding motifs (C-box and IR) and occurs simultaneously with APC/CAma1mediated Cdc20p degradation. Conclusions: Unlike the cyclical nature of mitotic cell division, meiosis is a linear pathway leading to the production of quiescent spores. This raises the question of how the APC/C is reset prior to spore germination. This and a previous study revealed that Cdc20p and Ama1p direct each others degradation via APC/C-dependent degradation. These findings suggest a model that the APC/C is inactivated by mutual degradation of the activators. In addition, these results support a model in which Ama1p and Cdc20p relocate to the substrate address within the APC/C cavity prior to degradation. Keywords: Cdc20p, Ama1p, Anaphase Promoting Complex, Meiosis
Background Meiosis is a specialized developmental program during which diploid nuclei undergo two consecutive meiotic divisions to produce haploid gametes. In the budding yeast, spore wall assembly follows the second meiotic nuclear division producing four haploid spores encased in a protective ascus [1]. Similar to differentiation programs in higher eukaryotes, meiotic progression is regulated by the transient expression of genes that are either * Correspondence: [email protected] 2 Department of Molecular Biology, UMDNJ-SOM, 2 Medical Center Drive, 08084, USA Full list of author information is available at the end of the article
meiosis specific or expressed during both meiotic and mitotic divisions (reviewed in [2]). In addition, progression through the meiotic divisions is also driven by the degradation of key regulatory proteins directed by the highly conserved multi-complex ubiquitin ligase called the anaphase promoting complex/cyclosome (APC/C) (reviewed in [3-6]). During meiosis, the APC/C is sequentially activated by two of the three known Trp-As
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