Functional cooperation between FACT and MCM is coordinated with cell cycle and differential complex formation.
BACKGROUND
Functional cooperation between FACT and the MCM helicase complex constitutes an integral step during DNA replication initiation. However, mode of regulation that underlies the proper functional interaction of FACT and MCM is poorly understood.


RESULTS
Here we present evidence indicating that such interaction is coordinated with cell cycle progression and differential complex formation. We first demonstrate the existence of two distinct FACT-MCM subassemblies, FACT-MCM2/4/6/7 and FACT-MCM2/3/4/5. Both complexes possess DNA unwinding activity and are subject to cell cycle-dependent enzymatic regulation. Interestingly, analysis of functional attributes further suggests that they act at distinct, and possibly sequential, steps during origin establishment and replication initiation. Moreover, we show that the phosphorylation profile of the FACT-associated MCM4 undergoes a cell cycle-dependent change, which is directly correlated with the catalytic activity of the FACT-MCM helicase complexes. Finally, at the quaternary structure level, physical interaction between FACT and MCM complexes is generally dependent on persistent cell cycle and further stabilized upon S phase entry. Cessation of mitotic cycle destabilizes the complex formation and likely leads to compromised coordination and activities.


CONCLUSIONS
Together, our results correlate FACT-MCM functionally and temporally with S phase and DNA replication. They further demonstrate that enzymatic activities intrinsically important for DNA replication are tightly controlled at various levels, thereby ensuring proper progression of, as well as exit from, the cell cycle and ultimately euploid gene balance.
Tan
Bertrand Chin-Ming
BC
Department of Life Science, College of Medicine, Chang Gung Univeristy, Taoyuan, Taiwan. btan@mail.cgu.edu.tw
Liu
Hsuan
H
Lin
Chih-Li
CL
Lee
Sheng-Chung
SC
D002453:Cell Cycle; D049109:Cell Proliferation; D002478:Cells, Cultured; D004265:DNA Helicases / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006609:High Mobility Group Proteins / Q000378:metabolism*; D006801:Humans; D035602:Transcriptional Elongation Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; C073537:SSRP1 protein, human; D035602:Transcriptional Elongation Factors; D004265:DNA Helicases