DNA replication requires a dedicated enzyme to unwind the duplex ahead of the DNA polymerase traveling in its wake. In bacteria, this role is served by DnaB, a hexameric ring helicase that is positioned at replication origins by the helicase loader DnaC, an AAA+ ATPase that works with initiation-factor DnaA to form a prereplication complex. The closed-ring architecture of DnaB prompts the question of how DnaC loads it onto the template, whether by promoting ring assembly around the DNA or by opening the ring to thread the template through. The structure of the Escherichia coli DnaB–DnaC complex recently reported by Berger and colleagues provides clear evidence for the latter. A combination of EM and SAXS shows that, whereas the apo form of DnaB is a closed ring, the DnaB–DnaC complex forms a spiral structure with a cracked ring and a central channel that is potentially accessible to DNA. Six DnaC subunits engage and open the DnaB hexamer, which is positioned such that its N-terminal domains form a collar around one end of the channel while its motor domains contact the DnaC N termini. Intriguingly, the AAA+ domains of DnaC are arranged in a spiral configuration characteristic of polymerase sliding-clamp loaders, which perform an analogous ring-opening function through their ATPase domains. However, in this case, DnaC's AAA+ domain is dispensable for DNA loading and unwinding in vitro, which suggests that DnaB remodeling involves distinct ATP-independent interactions with the DnaC N terminus to form the loading complex. ATP hydrolysis may instead help destabilize the DnaB collar and enhance transition to a translocation-competent conformation. Future determination of DNA-bound complex structures will help to define the role of the DnaB collar in regulating helicase activity and reveal potential similarities with the eukaryotic hexameric helicase, MCM2-7. (Cell 153, 438–448, 2013)