Fig. 1.

Composition and structure of the SF3b complex. a Nomenclature of SF3b components. Names used in human (H. sapiens) and budding yeast (S. cerevisiae) counterparts are listed for comparison. b Schematic domain organization of SF3b components depicted in different colors (SF3b1, cyan; SF3b2, pink; SF3b3, yellow; SF3b4, orange; SF3b5, green; SF3b6, blue; and SF3b7, purple). Domains on each protein are labeled and colored in gray. UHM, U2AF homology motif; HEAT, Huntingtin, EF3, PP2A, and TOR1; PR, proline-rich; HID, HEAT interaction domain; BPA/B/C, β-propeller domain A/B/C; RRM, RNA recognition motif; ZnF, zinc finger. c Structure of the SF3b complex. The left panel displays the overall structure of the SF3b complex in cartoon mode with each component labeled. The SF3b complex appears like a flaming torch with SF3b1 on the upper flame part, SF3b3 on the lower torch part and other subunits dotted within or around. The modification-related residues of SF3b1 (Thr434), SF3b2 (Arg508), and SF3b7 (Lys29) are indicated with red circles and colored in black [73, 78, 79]. The right panel shows three views of the SF3b complex in surface mode. The seven SF3b components are colored the same as in b. Protein Data Bank (PDB) accession code for the depiction of the structures is 5Z56 [27]. d Conformation of the SF3b1 HEAT domain. Superimposition of two conformations of the HEAT domain with the open conformation colored in gray and the closed conformation in rainbow. PDB accession codes for the depiction of the structures are 5Z56 and 5IFE [17, 27]. e The structure of SF3b1 binding to U2 and the pre-mRNA intron. Expanded view of the boxed region showing the location of BS-A in a pocket formed by SF3b1 and SF3b7. Proteins are shown in surface mode and RNAs in cartoon. SF3b6, which is distant from BS-A in the structure, is also shown. The pre-mRNA intron is colored in olive and U2 in firebrick. Proteins are colored the same as in b, and PDB accession code for the depiction of the structures is the same as in c