Microtubule-membrane Interactions in Cilia

Tetrahymena ciliary membranes were prepared by four different techniques, and their protein composition was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), electron microscopy, and two-dimensional thinlayer peptide mapping . Extraction of the isolated cilia by nonionic detergent solubilized the ciliary membranes but left the axonemal microtubules and dynein arms intact, as determined by quantitative electron microscopy . The proteins solubilized by detergent included a major 55,000-dalton protein, 1-3 high molecular weight proteins that comigrated, on SDS-PAGE, with the axonemal dynein, as well as several, other proteins of 45,000-50,000 daltons . Each of the major proteins contained a small amount of carbohydrate, as determined by PASstaining; no PAS-positive material was detected in the detergent-extracted axonemes . The major 55,000-dalton protein has proteins quite similar to those of tubulin, based on SDS-PAGE using three different buffer systems as well as twodimensional maps of tryptic peptides from the isolated 55,000-dalton protein . To determine whether this tubulin-like protein was associated with the membrane or whether it was an axonemal or matrix protein released by detergent treatment, three different methods to isolate ciliary membrane vesicles were developed . The protein composition of each of these different vesicle preparations was the same as that of the detergent -solubilized material . These results suggest that a major ciliary membrane protein has properties similar to those of tubulin .