Fluorescently labeled RNAs for the real-time CPSF73 activity assay. (A) Sequences of the model histone pre-mRNA substrate (H2a*) with a 3′ FAM label and the U7 snRNA with a 5′ TAMRA label. Nucleotides in the HDE that are changed to form Watson–Crick base pairs with the U7 snRNA are shown in lower case. (B). Overall structure of the core of the U7 machinery (Sun et al. 2020b). The proteins are shown as cartoons as well as a transparent surface in gray. The H2a* pre-mRNA is in orange, and U7 snRNA in green. The 5′ end of the U7 snRNA and 3′ end of H2a* are in close proximity. The red arrowhead indicates the active site of CPSF73. Panel B produced with PyMOL (www.pymol.org).
