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. 2022 Jul 7;27(14):4365. doi: 10.3390/molecules27144365

Figure 7.

Figure 7

An r(G1AAAg) pentaloop that adopts a Z-turn rather than an expected U-turn. The Z-step is marked by a circled “Z” in both the secondary and tertiary structure of the ribosomal H35a tetraloop of the Haloarcula marismortui large ribosomal subunit (PDBid: 4V9F). This motif is conserved in all known ribosome structures. It can be considered as a “shapeshifting” motif exemplifying the ability of an r(GAAA) loop to switch from U-turns to Z-turns in specific environments [13,31]. Note that a U-turn is characterized by an s3OP2 phosphate…π contact between the first and third residue (not shown), while Z-turns are characterized by sO4′3 between the 3rd and 4th residue and Zanti-turns by sO4′5 between the 3rd and 4th residue (Figure S5).