Structure prediction from amino-acid sequences. (a) Apparent domain structure within a typical tektin polypeptide. The positions of some conserved residues, including the signature nonapeptide, are indicated in single-letter amino acid code above the diagram. For a detailed comparison of a range of sequences, see NCBI Conserved DOmains pfam03148 . (b) Predictions of coiled-coil segments from the amino-acid sequences of various tektins plus a typical lamin for comparison. The vertical scale in each plot is the probability (0.0 to 1.0) of a coiled-coil structure being formed [69, 70]. Horizontal lines above each stretch with a high probability indicate the relative phases of the heptad repeats; a 'stutter' thus revealed in the middle of the last coiled-coil of the lamin is a feature of all lamins and IFs . Its position corresponds to that of the tektin loop containing the conserved nonapeptide, whose minor sequence variations are shown in red. For all three sea urchin tektins whose structure has been studied in detail [5–7], predicted 8 nm long (56-residue) segments that may each lie alongside a tubulin heterodimer are indicated by horizontal red bars. Human tektin 1 (NP_444515); human tektin 2 (AAH35620); human tektin 3 (AAH31688); mouse tektin 4 (AAI17527); C. elegans tektin (AAA96184); Chlamydomonas tektin (BAC77347); Strongylocentrotus purpuratus (sea urchin) tektin A1 (NP_999787, GenBank: M97188); S. purp. B1 (NP_999789, GenBank: L21838); S. purp. tektin C1 (NP_999788, GenBank: U38523); Drosophila tektin A (NP_523577); Drosophila tektin C (NP_523940); mouse lamin B1 (NP_034851).