High-yield fabrication of DNA and RNA scaffolds for single molecule force and torque spectroscopy experiments.

Single molecule biophysics experiments have enabled the observation of biomolecules with a great deal of precision in space and time, e.g. nucleic acids mechanical properties and protein-nucleic acids interactions using force and torque spectroscopy techniques. The success of these experiments strongly depends on the capacity of the researcher to design and fabricate complex nucleic acid scaffolds, as the pertinence and the yield of the experiment strongly depend on the high quality and purity of the final scaffold. Though the molecular biology techniques involved are well known, the fabrication of nucleic acids scaffold for single molecule experiments still remains a difficult task. Here, we present new protocols to generate high quality coilable double-stranded DNA and RNA, as well as DNA and RNA hairpins with ~500-1000 bp long stems. Importantly, we present a new approach based on single-stranded DNAs annealing and show, using magnetic tweezers, that it is more efficient to generate complex nucleic acid scaffolds in larger amount and at higher purity than a standard PCR-digestion-ligation approach. The protocols we describe here enable the design of any sort of complex nucleic acid scaffold for single molecule biophysics experiments and will therefore be extremely valuable to the community.