Duplex precursor assembly in TMACl assessed by native PAGE. Lane 1, 4.0 × 10−5 mol/L (40 μM) SQ1A:SQ1B duplex; lane 2, mixture of 4.0 × 10−5 mol/L (40 μM) C1A:C1B duplex and 8.0 × 10−5 mol/L (80 μM) single-stranded C1A. C1A:C1B is a 39-mer blunt-end duplex used as a control. SQ1A:SQ1B is the 39-mer synapsable duplex with overhangs. Gel with a mass fraction of 12% acrylamide was run in 0.01 TMgTB buffer and imaged by UV shadowing.