Figure 1.

Locating Ta₆Br₁₂ Clusters

(A) Three z sections of an anomalous Patterson map calculated from the inflection data of a two wavelength anomalous dispersion experiment. Cross-peaks for all four major sites (origin, 1-2, 1-3, and 1-4) and for one minor site (1-6) can be seen on these sections, as well as a number of other cross-peaks.

(B) The major and minor Ta₆Br₁₂ binding sites within the ASU are respectively indicated by large and small magenta spheres and numbered. The four U1 snRNPs in the ASU (particles A, B, C, and D) are colored red, yellow, green, and blue, respectively, with protein shown as ribbon and RNA as cartoon. The Ta₆Br₁₂ clusters bind in cavities between protein and RNA. Major sites lie between SL4 nucleotides 138 and 139 of RNA and the Sm ring residues in the β1-β2 loop of SmB and the β3-β4 loop of SmD1. Minor sites are found between the long α helix of U1-C protein, near Trp41, and the base of SL3 of a NCS-related particle.