Interaction of the shortest isoform of tau protein (tau 3) With human 14-3-3 zeta was analyzed by means of native gel electrophoresis, chemical crosslinking and size-exclusion chromatography. Phosphorylation by cAMP-dependent protein kinase (Lip to 2 mole of phosphate per mole of tau 3) strongly enhanced interaction of tau 3 with 14-3-3. Apparent K-D of the complexes formed by phosphorylated tau 3 and 14-3-3 was close to 2 mu M, whereas the Corresponding constant for unphosphorylated tau 3 was at least 10 times higher. The stoichiometry of the complexes formed by phosphorylated tau 3 and 14-3-3 was variable and was different from 1:1. 14-3-3 decreased the probability of formation of chemically crosslinked large homooligomers of phosphorylated tau 3 and at the same time induced formation of crosslinked heterooligomeric complexes of tau 3 and 14-3-3 with an apparent molecular mass of 120-140 kDa. All rights reserved. (C) 2009 Elsevier Inc. All rights reserved.