Investigating direct interaction between Escherichia coli topoisomerase I and RecA.

Protein-protein interactions are of special importance in cellular processes, including replication, transcription, recombination, and repair. Escherichia coli topoisomerase I (EcTOP1) is primarily involved in the relaxation of negative DNA supercoiling. E. coli RecA, the key protein for homologous recombination and SOS DNA-damage response, has been shown to stimulate the relaxation activity of EcTOP1. The evidence for their direct protein-protein interaction has not been previously established. We report here the direct physical interaction between E. coli RecA and topoisomerase I. We demonstrated the RecA-topoisomerase I interaction via pull-down assays, and surface plasmon resonance measurements. Molecular docking supports the observation that the interaction involves the topoisomerase I N-terminal domains that form the active site. Our results from pull-down assays showed that ATP, although not required, enhances the RecA-EcTOP1 interaction. We propose that E. coli RecA physically interacts with topoisomerase I to modulate the chromosomal DNA supercoiling.