RECQ1's double duty

The RECQ1 helicase can unwind DNA or stitch it back together. Which job the protein performs depends on how much help it gets, say Laura Muzzolini, Alessandro Vindigni (International Centre for Genetic Engineering and Biotechnology, Trieste, Italy), and colleagues. Unwinding is the job of single molecules or dimers, whereas oligomers of five or six enzymes take on annealing.

RECQ1 peels open DNA to permit replication and transcription. Why it also reseals strands isn't certain, but it may be assisting with repair. A further mystery is how the same molecule pulls off these two opposing tasks.

The team found that RECQ1 comes in two versions: a small form that's a monomer or a dimer; and a hefty size composed of pentamers or hexamers. Mixing in single-stranded DNA pushed the balance toward the larger...