Lipfert, J. et al. Nat. Commun. 2:439 (2011).

Magnetic tweezers are useful tools to study cellular processes such as replication, transcription, repair and protein binding to DNA, at the single-molecule level. Conventional setups, however, do not allow rotational motion to be tracked directly. Lipfert et al. now describe freely orbiting magnetic tweezers, which allow changes in the twist of nucleic acids to be measured, and use them to monitor assembly of recombination protein A filaments on DNA.