text: Several human and yeast snRNP structures were determined by the cryo-electron microscopy and successive single particle analysis.
  Recently, the human U1 snRNP core structure was determined by X-ray crystallography (3CW1, 3PGW), followed by a structure of the U4 core snRNP (2Y9A), which yielded first insights into atomic contacts, especially the binding mode of the Sm proteins to the Sm site. The structure of U6 UsnRNA was solved in complex with a specific protein Prp24 (4N0T), as well as a structure of its 3'-nucleotides bound to the special Lsm2-8 protein ring (4M7A). The PDB codes for the respective structures are mentioned in parentheses.
  The structures determined by single particle electron microscopy analysis are: human U1 snRNP, human U11/U12 di-snRNP,
  human U5 snRNP, U4/U6 di-snRNP, U4/U6∙U5 tri-snRNP.
  The further progress determining the structures and functions of snRNPs and spliceosomes continues.