In bacterial replication initiation, which statement describes how the DnaB helicase is loaded onto DNA after origin melting?

• A. DnaA directly loads DnaB.
• B. DnaC loads DnaB onto DNA.
• C. DnaB loads onto DNA without assistance.
• D. DnaA and DnaC together load DnaB onto DNA.

Answer: (C)

After the origin is melted by DnaA-ATP, the DnaB helicase cannot simply bind on its own. It is delivered and loaded onto the exposed single-stranded DNA by the helicase loader DnaC. DnaC binds DnaB and guides the complex to the melted origin, using ATP-driven steps to place DnaB onto the DNA; once loaded, DnaC dissociates and DnaB becomes the active helicase that unwinds the DNA in cooperation with DnaG primase to synthesize RNA primers. This loader-assisted delivery ensures correct positioning and activation of the helicase. So, loading the helicase without any assistance does not fit the established mechanism.