Studies of tektin filaments from flagellar microtubules by immunoelectron microscopy

Chemically resistant 2-3 nm filaments with a high alpha-helical content, isolated from sea-urchin sperm flagellar doublet microtubules, consist of proteins that have been named tektins. Polyclonal affinity-purified antibodies to tektins labelled sperm tails all along their lengths, as shown by indirect immunofluorescence microscopy, provided the specimens were not too well fixed. Results obtained for unfixed specimens studied by immunoelectron microscopy suggested the tektins are normally masked by tubulin. A monoclonal anti-tektin antibody labelled bare tektin filaments at longitudinal intervals of approximately 48 nm, which fits in well with the 96 nm longitudinal repeat of axonemes. We discuss a possible scheme for the regular interaction of tubulin monomers with an alpha-helical coiled coil.