Structural features of the Tetrahymena BB and comparison to other species. (A) Structure of TMTs from the proximal region of the BB from Tetrahymena (this work), Paramecium (EMDB_10729), and Chlamydomonas (EMDB_ 9167). Arrowheads denote structural features of the proximal region: A–C linkers (dark green), pinhead (cyan), A–B inner junction (magenta), and B–C inner junction (yellow). (B) Structure of TMTs from the central core region of the BB from Tetrahymena (this work), Paramecium (EMDB_4926), and Chlamydomonas (EMDB_ 4930). Arrowheads denote structural features of the core region: inner scaffold (lavender), A03 attachment site (teal) A–B inner junction inner scaffold attachment site (magenta) and B–C inner junction inner scaffold attachment site (yellow). Opaque teal arrowhead with a dashed outline in the Chlamydomonas core region structure indicates a missing A03 attachment. (C) CryoET structure of the whole wild-type BB in the core region, using the TMT structure from 100% of subtomograms, which shows partial loss of the C-tubule.