G1 M

S

G2

R

p53

Direct p21 transcription

Inactive CDK T P

T-loop

ATP 161 14 CDK

PSTAIRE NH2 T Y 15

p21

G1 Arrest

Cell cycle arrest mediated by p53 target p21 (WAF1)

DNA damage

El-Deiry et al., Cell 75:817, 1993

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