Cdk5-phosphorylated, but not CKII-phosphorylated, PrP is resistant to PK. A, Autoradiogram of Cdk5-phosphorylated PrP incubated with 0–10 μg/ml PK for 1 h at 4°C or 37°C. B, Autoradiogram of Cdk5-phosphorylated PrP incubated with 0–50 μg/ml PK for 4 h at 37°C. C, Autoradiogram of Cdk5- or CKII-phosphorylated PrP incubated with 0 or10 μg/ml PK for 1 h at 37°C.