Fork pausing complex engages topoisomerases at the replisome.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Replication forks pause at difficult genomic regions.
• Tof1-Csm3 acts as a molecular brake, while Rrm3 removes protein obstacles.

Purpose of the Study:

• Investigate the mechanism of Tof1-Csm3-mediated replication fork pausing.
• Determine the role of topoisomerases in fork regulation.

Main Methods:

• Yeast genetics
• Protein-DNA interactions
• Replication fork analysis

Main Results:

• Tof1-Csm3 recruits topoisomerase I (Top1) to promote fork pausing, independent of Rrm3.
• Topoisomerase II (Top2) partially compensates for Top1 loss.
• Tof1's C terminus is crucial for Top1 recruitment and pausing, but not checkpoint activation.

Conclusions:

• Replication forks pause at proteinaceous barriers via a "sTOP" mechanism involving topoisomerases I and II.
• This mechanism contributes to cellular protection against topoisomerase-inhibiting agents.