FIGURE 1.

The human pre-B spliceosome and interaction of SNU66 and SNRP27. Coordinates are of the human pre-B complex 6QX9 (Charenton et al. 2019) from the Protein Data Bank (PDB) as rendered in ChimeraX. The top image is the pre-B spliceosome and the bottom is a zoomed-in area in the same orientation showing the SNU66 and SNRP27 interaction. In the top image, PRP8 is in cornflower blue while U1 snRNA is dark blue and the pre-mRNA is orange. The U1 snRNA:5′ss helix is circled with a dotted line. In the bottom image, SNU66 is in green, SNRP27 is in red and PRP8 is in cornflower blue. The key interacting amino acids are labeled. The U4/U6 quasi-pseudoknot is shown stacking above SNU66 H734. The unstructured ACAGAGA region of U6 is indicated by the dashed line in the image.