RecA protein activates the E. coli topoisomerase III catenation function: essential role of the RecA ATPase.

RecA ATPase activity enables Escherichia coli topoisomerase III to rapidly convert circular ssDNA and partially homologous circular supercoiled DNA into catenanes and hemicatenanes within 1–2 min.

• Why it matters: Post-replication gaps must be resolved quickly under topological constraints, and the study addresses how RecA-driven strand exchange is functionally coordinated with topoisomerase III.
• What they did: The authors reconstituted RecA-mediated strand exchange using circular DNA substrates lacking free ends, then tested topoisomerase III alone versus combined with RecA, tracking catenation/hemicatenation kinetics and coupling to RecA ATP hydrolysis.
• The result: Together, RecA and topoisomerase III produce a robust, quantitative conversion to catenanes and hemicatenanes, tightly coupled to RecA ATP hydrolysis rate and requiring the ssDNA substrate.

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