Temperature-dependent expression of ciliary GPI-proteins in Paramecium.

Many eukaryotic membrane proteins have now been found to be anchored to the plasma membrane via a glycosylphosphatidylinositol membrane anchor (GPI-anchor). In Paramecium aurelia, a free-living ciliated protozoan, the major membrane protein, the surface antigen (SAg), is a GPI-anchored protein. This surface protein belongs to a multigene family, the expression and antigenic variation of which is controlled by environmental conditions. In order to screen for other Paramecium GPI-anchored proteins to identify those whose expression is also variable and influenced by external factors, we established a protocol permitting the rapid identification of GPI-proteins. The protocol is based upon the property of bacterial PI-PLCs to specifically release GPI-proteins. To overcome the resistance displayed by living paramecia to exogenous PI-PLCs, we used cilia purified from 35S-labeled cells obtained from various geographical strains grown under similar or different conditions. We observed a temperature-dependent variation in the electrophoretic patterns, as revealed by autoradiography of ciliary PI-PLC-releasable proteins from strain 513 of Paramecium primaurelia. In addition to a high molecular mass band corresponding to SAg molecules, three bands varying in apparent molecular mass from 30 to 50 kDa were observed at 23 degrees C. At 32 degrees C only one band of about 45 kDa was observed. Biosynthetic labeling experiments and the detection of the cross-reacting determinant after PI-PLC treatment (results reported elsewhere) provided definitive proof that these ciliary PI-PLC releasable proteins were actually GPI-proteins.(ABSTRACT TRUNCATED AT 250 WORDS)