Answer:
Mutations affecting proteins involved in the ubiquitination pathway
Explanation:
The cyclins represent a group of proteins capable of regulating the progression of the cell cycle via activation of cyclin-dependent kinases (CDKs). Cyclins are degraded by ubiquitination, a posttranslational modification that triggers the exit of mitosis by "marking" cyclin proteins for their subsequent degradation in the proteasome. The proteasome is a macromolecular complex required for the degradation of proteins in the cell. Then consequently the mutations affecting both secondary proteins required during ubiquitination and those involved in the functioning of the proteasome complex might prevent the degradation of cyclin proteins.