Mitotic cyclin is an example of a protein that is selectively degraded at a particular point in the cell cycle, namely the onset of anaphase. Suppose that you use recombinant DNA techniques to create a mutant form of mitotic cyclin that is not degraded at the onset of anaphase. Part A Sequence analysis of the mutant mitotic cyclin shows that it is missing a stretch of nine amino acids near one end of the molecule. Based on this information, discuss the possible explanations of why this form of mitotic cyclin is not degraded at the onset of anaphase. Select all that apply.
a. The missing segment contains a proteasome whose detection by an appropriate recognition protein normally targets mitotic cyclin for ubiquitination
b. The removal of a stretch of amino acids could change the conformation of mitotic cyclin so that it can no longer serve as a substrate for the ubiquitylating enzyme complex.
c. The removal of a stretch of amino acids could change the conformation of ubiquitin so that it can no longer form the ubiquitylating enzyme complex.
d. The missing stretch of amino acids contains the lysine to which ubiquitin is normally attached when mitotic cyclin is being targeted for destruction.
e. The missing stretch of amino acids contains the cysteine to which ubiquitin is normally attached when mitotic cyclin is being targeted for destruction.
f. The missing segment contains a degron whose detection by an appropriate recognition protein normally targets mitotic cyclin for ubiquitylation.

It is likely that the lack of nine amino acids in the C-terminus or the N-terminus of the cyclin protein affects its function. In general, these protein regions undergo post-translational modifications (such as phosphorylation or ubiquitination) that act as control points in signaling pathways

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