Tau in paired helical filaments is functionally distinct from fetal tau: assembly incompetence of paired helical filament-tau.

tau in paired helical filaments (PHF-tau) and fetal tau share several phosphorylated epitopes, as revealed by several phosphorylation-dependent PHF monoclonals. We have asked whether there is any difference between the two molecules in tubulin assembly-promoting activity and found that PHF-tau is almost assembly incompetent, whereas fetal tau is low in this activity but still assembly competent. This indicates that despite substantial similarities in immunoreactivities, PHF-tau and fetal tau are quite distinct from each other in function.