Discovery and binding site identification of a single-stranded DNA-binding protein that interacts with double-stranded DNA

Scientists have conducted in-depth studies on single-stranded DNA (ssDNA) binding and protein interaction network of single-stranded DNA binding proteins (SSBs). SSBs are widely present in cells from lower prokaryotes to higher mammals and are important proteins for ssDNA protection. In-depth studies in recent years have revealed a wide range of interactions between SSBs and other proteins. Studies have shown that in addition to playing the role of ssDNA protector, SSBs are also important members of biochemical pathways such as DNA replication and recombination. In this study, a single-stranded DNA binding protein SSF encoded by E. coli F plasmid with highly conserved N-terminal region was demonstrated to have ssDNA binding ability similar to E. coli SSB through gel migration experiments. At the same time, the dsDNA binding ability of SSF was also demonstrated, and the dissociation constant of this interaction (in the range of microliters) was determined by Micro-scale Thermophoresis (MST). Through the above experiments, a previously unreported SSB with dsDNA binding ability was revealed, and the region interacting with dsDNA was determined to be the C-terminal unstructured region. This study lays a foundation for further understanding of the mechanism of bacterial conjugation conducted by F plasmid, as well as the potential dsDNA binding ability and biological significance of other SSBs.