Cyclin A Vs Cyclin B

  • Both Cyclin A and Cyclin B are considered mitotic cyclins. Both cyclins are synthesized and degraded around the same time (Cyclin B is both synthesized and destroyed slightly later than cyclin A). 
  • Cyclin A accumulation starts at the late G1 phase and continues through S and G2 phases. The degradation of cyclin A in human cells starts in early prometaphase and is completed at metaphase. However, Cyclin B accumulation starts at the late S phase and continues in the G2 phase. The degradation of cyclin B starts at the end of metaphase (or just before anaphase) (Fung and Poon, 2005).
  • Transcriptional and proteolysis mechanisms are primarily responsible for the regulation of the expression of both cyclin A and cyclin B. 
  • Cyclin A functions in the S phase, however, its role in mitosis is still not completely understood. Cyclin B has an important role in M-phase entry as well as in M-phase progression.  
  • Cyclin B can activate only CDK1. However, cyclin A can activate both CDK1 and CDK2.

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