(A and B) 2D class averages from negatively stained images of SgrAI (bottom) and corresponding reconstructed density maps generated using the random-conical tilt reconstruction strategy (top) for dimeric and filamentous SgrAI. (A) A single SgrAI DBD with the corresponding crystal structure [48] displayed above. (B) Oligomeric SgrAI assembled into filaments of increasing sizes ranging from 2-DBDs to 13-DBDs. From these reconstructions, it was possible to visualize the helical nature of the filament and approximate the helical parameters that were subsequently used for high-resolution refinement from cryo-EM data. Scale bars represent 150 Å. Figure from ref. [45].