The presynaptic nucleoprotein filament of K23A/R33A mutant protein is defective in dsDNA capture. (A) Scheme of assay for examining DNA capture by presynaptic nucleotide protein filaments. See the main text and Materials and Methods for a detailed description. BSA was used as a negative control for ssDNA binding. R243A/K245A was a negative control for dsDNA capture by a presynaptic nucleoprotein filament. (B) SDS-PAGE analysis. RecA and BSA protein in "S1" and "B" were separated by electrophoresis in a 10% reducing polyacrylamide gel, and visualized by staining with Coomassie blue. (C) DNA agarose gel. For better quantitation, one-third or one-twelfth of the dsDNA (300 bps in length) in "S2" or "B" were separated on a 1% agarose gel, stained with ethidium bromide and then visualized by UV illumination.