A Helicase with an Extra Spring in Its Step

DNA replication requires hexameric ring-shaped helicases that unwind double-stranded DNA. In this issue, Itsathitphaisarn et al. report a high-resolution crystal structure of DnaB in complex with single-stranded DNA and nucleotide triphosphate analogs, revealing a unique mechanism by which DnaB unwinds DNA two base pairs at a time.