THE ROLE OF TAU PHOSPHORYLATION IN TRANSFECTED COS-1 CELLS

Tau cDNAs from each of the six human isoforms were transfected into CO S- 1 cells and, in every case, more than one peptide was observed. The diversity of expressed isoforms was due to different levels of tau ph osphorylation. Tau phosphorylation results in a decrease of the protei n electrophoretic mobility. The major contribution to this mobility sh ift is due to the phosphorylation at the at the C-terminus of the mole cule, as inferred from the expression of tau fragments. Phosphorylatio n takes place in some of the sites modified in neural cells and in the basis of AD patients. Copolymerization studies indicate that the leve l of phosphorylation, as well as the localization of the modified resi dues, may affect the binding of the protein to microtubules. These res ults indicate that phosphorylation regulates tau function inside the c ell.