The Smc5/6 complex is a DNA loop-extruding motor.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Structural Maintenance of Chromosomes (SMC) protein complexes are crucial for organizing chromosomes.
• While cohesin and condensin are known to organize DNA via loop extrusion, the function of the Smc5/6 complex is largely uncharacterized.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the function of the eukaryotic Smc5/6 complex.
• To determine if Smc5/6 utilizes DNA loop extrusion for chromosome organization.

Main Methods:

• Single-molecule imaging techniques were employed to observe Smc5/6 activity in real-time.
• ATP hydrolysis and its effect on DNA interaction were analyzed.

Main Results:

• Smc5/6 was demonstrated to form DNA loops through an active extrusion mechanism.
• The complex extrudes DNA loops at a rate of 1 kilobase pair per second, dependent on force and ATP hydrolysis.
• Dimeric Smc5/6 extrudes loops, while monomeric forms translocate unidirectionally along DNA.
• The Nse5/6 subunits were identified as negative regulators, inhibiting loop extrusion initiation by preventing Smc5/6 dimerization.

Conclusions:

• The Smc5/6 complex functions through DNA loop extrusion, similar to cohesin and condensin.
• DNA loop extrusion is a conserved mechanism across eukaryotic SMC complexes.
• Nse5/6 subunits play a regulatory role in Smc5/6-mediated loop extrusion initiation.