Background:Male germ cell RacGTPase activating protein (MgcRacGAP) is an important regulator of the Rho family GTPases - RhoA, Rac1, and Cdc42 - and is indispensable in cytokinesis and cell cycle progression. Inactivation of RhoA by phosphorylated MgcRacGAP is an essential step in cytokinesis. MgcRacGAP is also involved in G1-S transition and nuclear transport of signal transducer and activator of transcription 3/5 (STAT3/5). Expression of MgcRacGAP is strictly controlled in a cell cycle-dependent manner. However, the underlying mechanisms have not been elucidated.Methodology/Principal Findings:Using MgcRacGAP deletion mutants and the fusion proteins of full-length or partial fragments of MgcRacGAP to mVenus fluorescent protein, we demonstrated that MgcRacGAP is degraded by the ubiquitin-proteasome pathway in the late M to G1 phase via APCCDH1. We also identified the critical region for destruction located in the C-terminus of MgcRacGAP, AA537-570, which is necessary and sufficient for CDH1-mediated MgcRacGAP destruction. In addition, we identified a PEST domain-like structure with charged residues in MgcRacGAP and implicate it in effective ubiquitination of MgcRacGAP.Conclusions/Significance:Our findings not only reveal a novel mechanism for controlling the expression level of MgcRacGAP but also identify a new target of APCCDH1. Moreover our results identify a C-terminal region AA537-570 of MgcRacGAP as its degron.
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