Figure 2. Structures of Brr2^HR and Brr2^HR–Prp8^Jab1 complexes. (A) Domain organization of human Brr2. Domain coloring is conserved in all subsequent panels. Numbers indicate first and last residues of each domain. NE, N-terminal extension; L, linker. (B) Overall structure of human Brr2^HR (PDB ID 4F91). SL, separator loop. Domains and functional elements are labeled. (C) Model of a portion of U4/U6 snRNA bound to Brr2^HR. Arrow, putative breakpoint between the N-terminal RecA-2 and HB domains to allow RNA loading. Rotated 150° about the vertical axis compared with (B) as indicated. (D) Structure of the human Brr2^HR–Prp8^Jab1 complex (PDB ID 4KIT). C-terminal cassette orientated as in (B). The Brr2 N-terminal cassette is colored by domain as above. Conserved RNA-binding elements in the tunnel of the N-terminal cassette, brown; C-terminal cassette, light brown; hPrp8^Jab1, gold with semi-transparent surface. (E) Structure of the yeast Brr2^HR–Prp8^Jab1 complex (PDB ID 4BGD). C-terminal cassette orientated as in (B and D). Panels A–C adapted from reference 27 with changes; panel C adapted from reference 42.