A. SF-IV – G. stearothermophilus DnaB bound to ssDNA and GDP•AlF4 (PDB 4ESV). B. SF-V – E. coli Rho bound to ADP•BeF3 and RNA (PDB 3ICE). C. SF-III – papillomavirus E1 bound to ADP and ssDNA (PDB 2GXA). D. SF-VI – D. melanogaster Mcm2-7 bound to ADP, ATP and ssDNA (PDB 6RAZ). For all – Top: Top-down view of hexameric rings and active sites (inset). Bottom: Side view showing N-and C-terminal domains. RF = Arginine Finger, WA = Walker A, WB = Walker B, CE = Catalytic Glutamate, SI = Sensor I, SII = Sensor II.