A-D. Western blot analyses with 3F4, phospho-tyrosine (pTyr), anti-pPrPS43 and β-actin on phospho-column fractionated proteins from PrP/Cdk5/p25 co-transfected N2a cells (A), roscovitine-treated PrP/Cdk5/p25 co-transfected N2a cells (B), PrP S43A/Cdk5/p25 co-transfected N2a cells (C), PrP-transfected N2a (D), or untransfected N2a cells (E).