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. Author manuscript; available in PMC: 2024 Mar 27.
Published in final edited form as: Nat Struct Mol Biol. 2023 Dec 6;31(1):179–189. doi: 10.1038/s41594-023-01150-0

Extended Data Fig. 8. Structural basis for the conservation of the branch-site adenosine.

Extended Data Fig. 8

a. For the WT T.el4h intron, the branch-site adenosine A860 (yellow) forms a cis Watson-Crick:sugar edge pair with C858. The geometry of the hydrogen bonds making up this interaction are shown by yellow dashes and the distances are displayed in Å (black). b. If A860 is mutated to a guanosine (A860G) a hydrogen bonding clash (red arks) would form between the O2 of C858 and the O6 G860. c. In the case where A860 is mutated to a cytosine (A860C), the smaller pyrimidine nucleobase does not allow the N3 or N4 of the cytosine to effectively interact with C858 (red X). d. Lastly, if A860 was mutated to a uridine (A860U) a combination of noncomplementary hydrogen bonding and long interacting distances would lead to mispositioning of the branching nucleophile.