During mitosis, the breakdown of the nuclear envelope depends on the disassembly of

lamin filaments that form a meshwork supporting the membrane. How is that breakdown

accomplished?

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Bunny GreenfelderLv2

28 Jun 2019

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50. You are studying how phosphorylation by the Cdc2 kinasecontrols nuclear lamina disassembly during mitosis. You make aseries of mutations in a gene encoding a lamin protein and expressthese mutated lamins inside the cell (ie the cell now makes themutated lamins). You find that when you mutate a serine residue onthe amino terminal domain of the nuclear lamin, the mutated proteinassembles into the nuclear
lamina just fine, but does not depolymerize during mitosis. Suggesta possible reason why this lamin protein might be resistant to Cdc2kinase-mediated disassembly.

For your responses please justify your answer. No justificationfor answer will recieve "needs work" rating.

32. Which statements concerning the regulation of CDK/cyclincomplexes are correct?
A. At different points in the cell cycle, G1 and mitotic cyclinscan activate the same CDK subunit.
B. Phosphorylation of CDK proteins can both activate and inhibitcyclin/CDK activity.
C. If CAK has phosphorylated the CDK subunit, CDKs will remainactive in the absence of cyclin.
D. The CDK/G1 cyclin complexes that control S phase initiation arelikely to have signal sequences
that target them for nuclear import.
F. Cyclin/CDK complexes are frequently targets of cell cyclecheckpoint pathways.

33. Which of the following statements concerningubiquitin-mediated proteolysis are correct?
A. Ubiquitin modification serves as a molecular âtagâ to signaldegradation by the proteosome.
B. Both G1 and mitotic cyclins are targets for ubiquitin-mediatedproteolysis.
C. Nuclear envelope breakdown during mitosis is accomplished byubiquitin-mediated
proteolysis of lamin intermediate filament proteins.
D. The separation of sister chromatids at the metaphase to anaphasetransition is controlled by
ubiquitin-mediated proteolysis of an anaphase inhibitor.
E. Conditional mutations that inactivate the gene encodingubiquitin in yeast would be expected
to exhibit a cdc phenotype.

Phosphorylation of nuclear lamins regulates their assembly and disassembly during mitosis. You add a drug to cells undergoing mitosis that inhibits the activity of an enzyme that dephosphorylates nuclear lamins. What do you predict will happen to these cells? Why?