In DNA replication, DnaG primase synthesizes RNA primers for both leading- and lagging-strand DNA synthesis. Lagging-strand DNA replication requires multiple primers for Okazaki fragment formation. Far fewer copies of DnaG molecules exist in a cell than the estimated number of priming sites. In Escherichia coli, lagging-strand synthesis therefore requires a DnaG-recycling mechanism, and a three-point switch model of primer handoff from primase to DNA polymerase has been proposed. This involves sequential protein-protein interactions of DnaG-DnaB (helicase), DnaG-SSB (single-stranded DNA-binding protein) and SSB-χ (a subunit of Pol III holoenzyme)¹. The interaction between DnaG and SSB occurs through the DnaGC domain and the SSB C-terminal peptide (SSBct), as demonstrated By SPR and the crystal structure of the DnaGC-SSBct complex. But the DnaGC-SSBct interaction cannot be detected with proteins from Gram +ve Staphylococcus aureus and Geobacillus stearothermophilus (Gst), or Gram –ve Acinetobacter baylyi and A. baummannii. The SSBct binding pocket is shallow in the crystal structures of DnaGC from A. baylyi and Gst. Also, DnaG and DnaB in Gst form a tight interaction through their DnaGC and DnaBN domains respectively ², but the interaction between the two domains in E. coli is transient ³. The differences of the interactions of DnaG with SSB and DnaB in different bacterial species suggest different regulatory mechanisms in RNA priming during lagging-strand DNA replication.