SUBPELLICULAR MICROTUBULES ASSOCIATE WITH AN INTRAMEMBRANOUS PARTICLELATTICE IN THE PROTOZOAN PARASITE TOXOPLASMA-GONDII

Application of Fourier analysis techniques to images of isolated, froz en-hydrated subpellicular microtubules from the protozoan parasite Tox oplasma gondii demonstrates a distinctive 32 nm periodicity along the length of the microtubules, A 32 nm longitudinal repeat is also observ ed in the double rows of intramembranous particles seen in freeze-frac ture images of the parasite's pellicle; these rows are thought to over lie the subpellicular microtubules. Remarkably, the 32 nm intramembran ous particle periodicity is carried over laterally to the single rows of particles that lie between the microtubule-associated double rows. This creates a two-dimensional particle lattice, with the second dimen sion at an angle of similar to 75 degrees to the longitudinal rows (de pending on position along the length of the parasite). Drugs that disr upt known cytoskeletal components fail to destroy the integrity of the particle lattice. intramembranous particle organization suggests exis tence of multiple cytoskeletal filaments of unknown identity. Filament s associated with the particle lattice provide a possible mechanism fo r motility and shape change in Toxoplasma: distortion of the lattice m ay mediate the twirling motility seen upon host-cell lysis, and morpho logical changes observed during invasion.