Hypothetical U1 snRNA–pre-mRNA complex structure. The main image represents the secondary structure depiction of the hypothetical U1 snRNA–pre-mRNA complex derived from the RNAcofold server. The inset images show the secondary structure and the tertiary structure generated from the same secondary structure prediction in closer detail. In the secondary structure (lower inset), the residues of U1 snRNA are shown in dark green, whereas the residues of the pre-mRNA participating in the interaction with U1 snRNA are red. The canonical base pairing is shown by lines, whereas noncanonical ones are represented by a blue dot. The tertiary structure (upper inset) is depicted in stick format. U1 snRNA is shown in light green, whereas the pre-mRNA interacting residues are red. The rest of the pre-mRNA is gray.