Paramecium GPI proteins: Variability of expression and localization

In Paramecium primaurelia, the two major classes of cell surface proteins, the surface antigen (SAg) and the surface GPI proteins (SGPs), are linked t o the plasma membrane through a glycosylphosphatidylinositol (GPI) anchor. In the present study, we have characterized the expression of the SGPs in s everal geographical strains of P. primaurelia and P. tetraurelia at differe nt temperatures, 23 degrees C and 32 degrees C. The identification of the e xpressed SGPs was performed on purified cilia, by establishing the SGP SDS- PAGE profiles under four different conditions: with or without their anchor ing lipid, cleaved with a Bacillus thuringiensis phosphatidylinasitol-speci fic phospholipase C (PI-PLC), and either in a reduced or in an unreduced st ate. This screening revealed the existence of specific sets of ciliary SGPs , as a function of temperature and the geographical origin of the strains. The SGPs the most abundant at 23 degrees C and 32 degrees C displayed a vap id turnover. We also looked for the presence of PI-PLC releasable proteins in purified cortices. In addition to the SAg and SGPs, the cortical fractio n was shown to contain other PI-PLC releasable proteins, not: found in the ciliary fraction, thus localized exclusively in the interciliary region.