The interactions at the decoding center. (a) Crystal structure of the 30S subunit (PDB code: 2J00). (b) Close-up of the decoding center in the absence of mRNA (PDB code: 1J5E). (c) Close-up of the decoding center in the presence of cognate mRNA (PDB code: 1IBM). (d) Close-up of the decoding center in the presence of a near-cognate mRNA (PDB code: 1N34). The structures are displayed in Ribbons. Labels and landmarks: sp, spur; bk, beak; h, head; S12, protein S12; DC, decoding center; h44, helix 44; A-tRNA/ASL, A-site tRNA ASL.