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. 2019 Nov;11(11):a032417. doi: 10.1101/cshperspect.a032417

Figure 3.

Figure 3.

Molecular organization of RNA−protein interactions involving the catalytic RNA network, 5′SS, and 5′ exon in the human Bact complex. (A) Overview of the structural organization of the human Bact complex. The positions of PPIases are circled in black. (B) Accommodation of the catalytic RNA network that is first formed in Bact by the PRP8 amino-terminal domain (NTD) and helical bundle (HB) domains and α-finger of its Linker domain. Part of RNF113A (Cwc24) and SF3A2 (Prp11) are inserted into the gap between the RT/En domain and the catalytic RNA network and these proteins are replaced by the U2/BS helix in the C complex (see insets). (C) Close-up of interactions between the 5′SS nucleotides G+1 and U+2 and residues of RNF113A, and between SF3A2 and G+1 and G−1. (D) PRP19/CDC5L complex proteins and related proteins directly contact primarily flipped-out U6 nucleotides in the catalytic RNA core. For example, the base of U6-C60 in the lower stem of the ISL lies in a pocket formed by amino acids of SYF3, CDC5L, RBM22, and SKIP (upper panel) and flipped-out U6-U68 of the U6 ISL loop is bound cooperatively by amino acids of PLRG1 and CWC15 (lower panel). (E) Spatial organization of the 5′ exon binding channel in hBact. Black circles indicate the position of PPIL2’s U box domains and CWC27’s PPIase domain. (F) U2/U6 helix II adopts a unique position in human (upper panel) compared with yeast (lower panel) Bact. In yBact, helix II lies in a more upright position and interacts with Syf2, whereas in hBact it lies more perpendicular (relative to the U6 ACAGA/5′SS helix) and contacts the PPIase domain of the PPIL2 protein, which is not present in the S. cerevisiae spliceosome. Black circle indicates the position of PPIL2’s PPIase domain.