Motor channel size and chirality as two distinguishing features of revolution and rotation motors. A. Rotation motors have a channel size smaller than 2 nm to allow full contact between channel wall and the single-stranded nucleic acid inside the channel. Revolution motors have channel sizes larger than 3 nm to provide enough space for the revolution motion. B. Rotation motors use a right-handed channel to drive the right-handed DNA through parallel threads, while revolution motors use a left-handed channel in an anti-chiral arrangement with the right-handed dsDNA during translocation. (Adapted from  with permission of BioMed Central, and adapted fromwith permission from Elsevier). (PDB IDs: RepA, 1G8Y; TrwB: 1E9R; ssoMCM, 2VL6; SV40-LTag, 1SVL; Rho, 3ICE; E1, 2GXA; T7-gp4D, 1E0J; FtsK, 2IUU; SPP1-gp6, 2JES; phi29-gp10, 1H5W; P22-gp1, 3LJ5; T4-gp17, 3EZK; DnaB, 4ESV; HK97 family-portal protein, 3KDR. EM IDs: T7-gp8, EMD-1231; MCM, EMD-1834).