Purification of the surface membrane-cytoskeleton complex (Cortex) of Paramecium and identification of several of its protein constituents.

In ciliates, the major morphogenetic events take place in the cortex, a complex of membranes and closely associated filamentous networks. To analyze the problems of assembly and morphogenesis at the molecular level in Paramecium, we have developed a method of purification of cortex fragments which retain their in situ organization and display a highly reproducible electrophoretic profile. The method used either a four-step sucrose gradient yielding a cortex + oral apparatus fraction or a six-step gradient which allowed the cortex fragments to be freed from the oral apparatuses (which were recovered separately). By comparative electrophoresis and immunological probing of these and other cell fractions or purified organelles, we could identify several of the major polypeptides resolved by SDS PAGE as components of specific cortical or oral structures. The purification method was successfully applied to morphological mutants, and the first case of a mutational modification of a cortical polypeptide was observed.