Three recurrent classes of polysomes display specific conformations. (a, left) Galleries of LMW, MMW, and HMW polysomes showing examples belonging to the three main classes obtained after KerDenSOM classification. (right) Schematic representations of possible ribosome arrangements typical of each class (from top to bottom: rounded, rectangular, and triangular). Bars, 100 nm. (b) Representative images of polysomes for each class are shown by 3D AFM projections (from left to right: triangular, rectangular, and rounded). (c) Representative images of polysomes for each class are shown by cryo-EM, where arrangements of ribosomes were determined by placing a consensus map of all the ribosomes imaged at the positions and in the orientations determined (40S in yellow, 60S in blue; from left to right: triangular, rectangular, and rounded).