Figure 1. Regulation of cyclin B accumulation. A combination of temporally regulated degradation and transcription ensures that cyclin B levels peak in late G2 phase and during early mitosis. After silencing of the spindle checkpoint in mitosis, cyclin B is degraded by the APC/C. APC/C activity maintains low cyclin B levels through G1 phase until silencing of APC/C in S phase by a combination of direct inactivation by cyclin A–Cdk2, binding of the inhibitor Emi1, and, possibly, autodestruction of the APC/C E2 ligase UbcH10. Starting in S phase and peaking in late G2 phase, accumulating cyclin A–Cdk2 activity also activates the transcription factors B-MYB, NF-Y, and FoxM1, which directly enhance cyclin B transcription. In addition to transcription and degradation, the local concentration of cyclin B is enhanced during centrosome maturation by Plk1- and Aurora A–dependent targeting of cyclin B to the centrosome.
Figure 1.

Regulation of cyclin B accumulation. A combination of temporally regulated degradation and transcription ensures that cyclin B levels peak in late G2 phase and during early mitosis. After silencing of the spindle checkpoint in mitosis, cyclin B is degraded by the APC/C. APC/C activity maintains low cyclin B levels through G1 phase until silencing of APC/C in S phase by a combination of direct inactivation by cyclin A–Cdk2, binding of the inhibitor Emi1, and, possibly, autodestruction of the APC/C E2 ligase UbcH10. Starting in S phase and peaking in late G2 phase, accumulating cyclin A–Cdk2 activity also activates the transcription factors B-MYB, NF-Y, and FoxM1, which directly enhance cyclin B transcription. In addition to transcription and degradation, the local concentration of cyclin B is enhanced during centrosome maturation by Plk1- and Aurora A–dependent targeting of cyclin B to the centrosome.

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