Figure 6.

Structural comparison of the cold shock domains. A–C, surface representation of the CSD of YB-1 (blue; A), human Lin28a (light purple, PDB 5UDZ; B), and mouse Lin28a (wheat, PDB 3TS2; C) in complex with RNA oligos. Only the tetranucleotides with two adjacent nucleotides are shown. Sequences of the nucleotides are unified with the CAUC consensus sequence. RNA oligos are shown in cartoon mode. D, recognition of U₃ and U₄ of pre-let-7f by hLin28a CSD. U₄ stacks over the five-membered ring of the indole moiety. There is no hydrogen bond between Lys-45 and U₃ or between Asn-48 and U₄. The corresponding Met-51 stands away from U₄, and no hydrogen bond is formed between Met-51 and the 2′-OH of U₄. E, recognition of U₃ and A₄ of pre-let-7g by mLin28 CSD. Asn-48 forms a hydrogen bond with the N³ of A₄. No hydrogen bond interaction exists between the 2′-OH of A₄ and Met-51.