FIG. 2.—

Eukaryotic Sm ring and Sm-anchored snRNP. (A) Human fixed class Sm ring anchoring spliceosomal snRNPs (see text). Reprinted from Kambach, Walke, Young, et al. (1999). ©1999 with permission from Elsevier. (B) Human U1 snRNP. Shown are the fixed Sm ring with its central pore; the U1 snRNA passing through the central pore of the ring with loops I, II, II, and IV and the Sm site in blue, red, green, orange, and yellow, respectively; and the locations of the 70K, U1-A, and B + C set of U1-associated proteins (Stark and Lührmann 2006). Figure kindly provided by H. Stark (Max Planck Institute for Biophysical Chemistry, Göttingen, Germany); labels added by authors.