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. Author manuscript; available in PMC: 2017 Jul 11.
Published in final edited form as: Nature. 2017 Jan 11;542(7641):377–380. doi: 10.1038/nature21078

Figure 2. Architecture of the RNA catalytic core in C* complex.

Figure 2

a, Key RNA structures at the active site. The branch helix has undocked from the catalytic Mg2+ site. BP, branch point; ISL, internal stem-loop; M1 and M2, catalytic metal ions. b, Rotated view showing superposition of the RNA catalytic core for the C (PDB, 5LJ5; ref. 4) and C* spliceosomes. C elements are coloured in light shades. Note substantial rotation of the branch helix between the two complexes. c, The BP and 5’-splice site nucleotides align in a path to the catalytic Mg2+ site. A possible intron path guiding the 3’-splice site to the Mg2+ site is shown as a dashed line. d, Watson-Crick-Hoogsteen interaction between U(+2) and A51 of U6 snRNA. e, Different interactions of U(+2) and A(+3) observed in C complex.