Fig. 1.

Architecture of the U6 snRNP from Saccharomyces cerevisiae. a Sequence and observed secondary structure of the U6 snRNA used for crystallization. Disordered nucleotides are shown in gray text, and the absent 5′ stem region is shown as a dashed line. The 30–113 nucleotide RNA that was used for crystallization has a 3′ phosphate group and A62G/A79G mutations (colored red) to quench structural dynamics in the U6 internal stem loop (ISL), which do not alter the core topology of the U6/Prp24 complex^22,23. The 30–112 RNA that yielded a different crystal form contains a 2′ phosphate group and lacks the A79G mutation. b Primary structure of protein components in U6 snRNP samples used for crystallization. The occluded (o) RRM4 of Prp24 has additional N- and C-terminal alpha helices appended to its RRM core⁷⁶, and is denoted as RRM4 hereafter. In PDB 5VSU, Prp24 residues 1–26 and 399–431 are disordered. In PDB 6ASO, Prp24 residues 1–27 are truncated; 28–29 and 399–444 are disordered. The C-terminus of Lsm4 is predicted to be disordered and was therefore truncated from the crystallization construct (Supplementary Note 1). c Overall architecture of the yeast U6 snRNP, as observed in two distinct crystal structures (Supplementary Table 1). U6 snRNA (red) and Prp24 (blue) contact the “proximal” face of the Lsm2-8 ring. d Alternate view of the U6 snRNP. The ~ 30-residue linker region between RRM4 and the C-terminal SNFFL box motif of Prp24 is disordered and depicted as a dashed line