FIG. 4.

Contacts of ring III of gentamicin C1a with the A-site oligonucleotide (23). The 2" hydroxyl group on ring III of gentamicin C1a forms a hydrogen bond with the O-4 of U1406 (shown in bold) and the 3" aminomethyl forms a hydrogen bond with the N-7 of G1405; these interactions are shown explicitly. In addition, the ring III 4" hydroxyl forms a hydrogen bond with the phosphate between G1405 and U1406 (not highlighted). Gentamicin is gray, and the RNA is beige. Oxygen, nitrogen, and phosphorus are red, blue, and yellow, respectively.