A3G multimers interact with ssDNA termini and mediate interstrand synapsis. (A-C) AFM images showing binding of purified 293T cell–derived A3G-His₆ to L_C ssDNA (A3G multimer:ssDNA molar ratio ∼ 1:1) after 1 minute (A), 5 minutes (B), and 30 minutes (Ci-ii) incubation on ice. (B) Insets: Three-dimensional representations of parts of the 2D image (orientation has been tilted for clarity). (Ci) Inset: magnification of dashed box area. (Ciii) A3G was incubated in the absence of ssDNA. M indicates A3G multimer; d, dimer; m, monomer; T, A3G multimer associated with ssDNA terminus; and IS, ssDNA interstrand synapse. (D) Quantitation of A3G-ssDNA complexes. Data are represented as mean ± SD from at least 10 different fields for each time point.