4E-BP1 (eIF4E-binding protein) also known as PHAS, is a 10-12 kDa acidic protein that compete with eIF4G for binding of eiF4E to the mRNA 5 cap structure (1). Binding of the 4E-BPs to eIF4E is reversible and is dependent on the phosphorylation status of 4E-BP. Non-phosphorylated 4E-BP1 will bind strongly to eiF4E while, the phosphorylated form will no (2)t. Akt, TOR, MAP kinase, S6 kinase, and Cdc2 are known kinases capable of inactivating 4E-BP1 binding to eIF4E by phosphorylating either threonines 35, 45, 69 or serine 65. Although, not all phosphorylation events equally block the 4EBP1-eIF4E interaction (3-4)

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