Fig. 3: Structural comparison between Drosophila and human ICM.

a Overlay of the overall structure of Drosophila ICM and human ICM in the structure of Integrator in complex with PP2A (PDB entry 7CUN). The positions of CTD2 of IntS9 and IntS11 are noticeably different, likely related to the flexibility in these domains. There are differences in the registering of residues in places, and many of the residues in human Integrator lack models for the side chain due to poor EM density. b Overlay of the overall structure of Drosophila ICM and human ICM (PDB entry 7BFP). The rms distances for equivalent Cα atoms of IntS11, IntS9, and IntS4 are 1.5, 1.3, and 1.6 Å, respectively. With IntS11 in overlay, the orientations of the IntS9 and IntS4 subunits in the two structures differ by 2.6 and 2.9° rotation. Two additional pairs of helices at the C-terminal end of IntS4 NTD are modeled in the Drosophila ICM (residues 500–570). Many loops on the surface of the two structures have different conformations (for example residues 300–317 of Drosophila IntS11), and some of the loops are missing in human ICM (such as residues 343–370 in IntS9). Conformational differences are also seen for the CTD1 complex, and the CTD2 of IntS9 and IntS11 are not modeled in the human ICM. Differences in registering are also observed, for example see Fig. 5c.