RRM1 and Azoospermia: We randomly chose five structures of other nucleic acid-bound RRM1 motifs, including human RBM45 [22] (PDB ID: 7CSZ), DAZL (azoospermia (DAZ)-like) [23] (PDB ID: 2XS5), hnRNP A1 [8] (PDB ID: 5MPG), U2AF2 [24] (PDB ID: 6XLW), and IMP3 [25] (PDB ID: 6GX6), for comparison (figure 3a,b).