Cyclins are a required component of cyclin-CDK complexes for regulated progression through the eukaryotic cell cycle. Most cyclins are progressively synthesized and then degraded systematically in a temporal fashion at various points in the cell cycle. As we discussed in Chapter 7, cellular protein expression can be regulated at several different points starting with initiation of gene transcription.

a. What type of assay(s) could be employed to determine whether the expression of cyclin B is regulated at the transcriptional or translational level, if either?

b. Based on what you've learned in Chapter 19, is it possible that the activity of cyclin B could be regulated at the post-translational level? Describe a cellular mechanism through which this might happen.

c. How might it be possible for cyclin B expression and/ or activity to be at least partially regulated by events in the cell's external environment?