ATP hydrolysis is required for cohesin's association with chromosomes.
BACKGROUND
A multi-subunit protein complex called cohesin is involved in holding sister chromatids together after DNA replication. Cohesin contains four core subunits: Smc1, Smc3, Scc1, and Scc3. Biochemical studies suggest that Smc1 and Smc3 each form 50 nm-long antiparallel coiled coils (arms) and bind to each other to form V-shaped heterodimers with globular ABC-like ATPases (created by the juxtaposition of N- and C-terminal domains) at their apices. These Smc "heads" are connected by Scc1, creating a tripartite proteinaceous ring.


RESULTS
To investigate the role of Smc1 and Smc3's ATPase domains, we engineered smc1 and smc3 mutations predicted to abolish either ATP binding or hydrolysis. All mutations abolished Smc protein function. The binding of ATP to Smc1, but not Smc3, was essential for Scc1's association with Smc1/3 heterodimers. In contrast, mutations predicted to prevent hydrolysis of ATP bound to either head abolished cohesin's association with chromatin but not Scc1's ability to connect Smc1's head with that of Smc3. Inactivation of the Scc2/4 complex had a similar if not identical effect; namely, the production of tripartite cohesin rings that cannot associate with chromosomes.


CONCLUSIONS
Cohesin complexes whose heads have been connected by Scc1 must hydrolyze ATP in order to associate stably with chromosomes. If chromosomal association is mediated by the topological entrapment of DNA inside cohesin's ring, then ATP hydrolysis may be responsible for creating a gate through which DNA can enter. We suggest that ATP hydrolysis drives the temporary disconnection of Scc1 from Smc heads that are needed for DNA entrapment and that this process is promoted by Scc2/4.
Arumugam
Prakash
P
Research Institute of Molecular Pathology (IMP), Dr. Bohr-Gasse 7, 1030 Vienna, Austria.
Gruber
Stephan
S
Tanaka
Koichi
K
Haering
Christian H
CH
Mechtler
Karl
K
Nasmyth
Kim
K
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D015153:Blotting, Western; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D002875:Chromosomes / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins; D006868:Hydrolysis; D008956:Models, Chemical; D009687:Nuclear Proteins / Q000378:metabolism*; D000097722:Cohesins
D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004247:DNA; D005656:Fungal Proteins; D009687:Nuclear Proteins; D000097722:Cohesins