Week 11: Cdc48/VCP Promotes Chromosome Morphogenesis By Releasing Condensin From Self-entrapment In Chromatin

Question 1

Highlights of the article

Answer 1

1. The condensin complex is the main effector of chromosome condensation in mitosis
2. Chromatin accessibility is reduced when chromosomes are compacted by condensin
3. Cdc48/VCP segregate stimulates condensin release from compacted chromatin: aka resolution
4. Condensin must maintain high mobility on mitotic chromatin to promote condensation

Question 2

What is the condensin complex/ how is it resolved

Answer 2

1. A highly conserved ring shaped ATPase
2. Composed of Smc2 and Smc4 ATPase subunits, HEAT repeat proteins and a kleisin subunit
3. Gets resolved by Cdc20/VCP/p97 which promotes ubiquitin dependant cyclin of condensin on mitotic chromatin

Question 3

What phosphorylates and activates condensin in mitosis

Answer 3

1. Mitosis: condensin is activated via cdk1 phosphorylation of smc4 which leads to initial steps of chromosome condensation
2. When cdk1 is later inactive in later mitosis, cdc5/polo kinase assumes the role of condensin phosphorylation to promote condensation

Question 4

What does condensing function depend on?

Answer 4

1. It’s ATPase activity: abrogation of ATP hydrolysis by cmv2 or smc4 is incompatiable w chromosome segregation and cell viability

Question 5

Active unloading mechanism

Answer 5

1. Suggested because condensin promotes chromosome condensation in cycles … therefore smth needs to remove it
2. Condensin needs to be unloaded efficiently

Question 6

What did they discover

Answer 6

1. Cdc48 works with its Ufd1-Npl4 cofactor to stimulate dynamic cycles of condensin unloading and loading to promote chromosome condensation

Question 7

Figure 1B

Answer 7

1. Objective: to determine effectors needed for condensation
2. FISH was used to locate the rDNA to see the condensin induced changed =loop (if puff=condensin defective=uncondensed)
3. Chromosome condensation defects in eas1, swr1, rvb2, and cdc48 mutants=show puff morphology therefore these WT are needed for condensation/line morphology

Question 8

Figure 2C

Answer 8

1. Ufd1-2 and npl4-1 mutants showed strong defects in chromosome morphology in mitosis
2. Concluded that Ufd1-npl4 dimer is the specific cofactor that assists cdc48 in the regulation of chromosome morphogenesis in mitosis.
3. Ufd and Npl both show puff=uncondensed chromosomes (condensin removed): when mutated, chromosomes are still condensed (line)
4. Conclusion: ufd1-npl4 dimer needed as a specific cofactor that assists cdc48 in regulation of chromosome morphogenesis in mitosis

Question 9

Figure 4A

Answer 9

1. RDNA morphology was analyzed by FISH in ubiquitination and SUMOlation deficient mutants
2. Ubiquitin defective mutant uba1=strong chromosome condensation defects (line/condensed still) versus uba1-204 which does condensation via ubiquitination (puff/uncondensed)
3. Cdc48 utilizes ubiquitination in condensation resolution