RAFT1 phosphorylates p70S6 kinase and 4E-BP1, which are key regulators of translation. The study shows that RAFT1 directly phosphorylates these proteins, with serum stimulating RAFT1 kinase activity similar to that of p70S6k and 4E-BP1 phosphorylation. RAFT1 phosphorylates p70S6k at Thr-389, a site whose phosphorylation is rapamycin-sensitive and necessary for S6 kinase activity. It also phosphorylates 4E-BP1 at Thr-36 and Thr-45, which blocks its interaction with eIF-4E, a cap-binding protein. Phosphorylation of Thr-45 is a major regulator of the 4E-BP1-eIF-4E interaction in vivo. RAFT1 phosphorylates p70S6k more effectively than 4E-BP1, and the phosphorylation sites on the two proteins show little homology. This suggests that an unidentified kinase similar to p70S6k may be activated by RAFT1 phosphorylation and act at the rapamycin-sensitive phosphorylation sites of 4E-BP1. The study also shows that RAFT1 phosphorylates p70S6k on Thr-389, which is essential for S6 kinase activity. Mutation of Thr-389 to alanine significantly reduces S6 kinase activity and prevents serum stimulation. RAFT1 phosphorylates 4E-BP1 on Thr-36 and Thr-45, which blocks its interaction with eIF-4E. Mutation of these sites to alanine causes 4E-BP1 to constitutively bind to eIF-4E, mimicking the effects of rapamycin. These findings indicate that RAFT1 plays a critical role in regulating the interaction between 4E-BP1 and eIF-4E, which is essential for cap-dependent translation. The study also highlights the importance of RAFT1 in the rapamycin-sensitive signaling pathway, which is involved in regulating protein synthesis in response to growth factors. The results suggest that RAFT1 is a key regulator of translation, and its phosphorylation of p70S6k and 4E-BP1 is essential for the proper functioning of the pathway. The study provides important insights into the molecular mechanisms underlying the regulation of protein synthesis and the role of RAFT1 in this process.RAFT1 phosphorylates p70S6 kinase and 4E-BP1, which are key regulators of translation. The study shows that RAFT1 directly phosphorylates these proteins, with serum stimulating RAFT1 kinase activity similar to that of p70S6k and 4E-BP1 phosphorylation. RAFT1 phosphorylates p70S6k at Thr-389, a site whose phosphorylation is rapamycin-sensitive and necessary for S6 kinase activity. It also phosphorylates 4E-BP1 at Thr-36 and Thr-45, which blocks its interaction with eIF-4E, a cap-binding protein. Phosphorylation of Thr-45 is a major regulator of the 4E-BP1-eIF-4E interaction in vivo. RAFT1 phosphorylates p70S6k more effectively than 4E-BP1, and the phosphorylation sites on the two proteins show little homology. This suggests that an unidentified kinase similar to p70S6k may be activated by RAFT1 phosphorylation and act at the rapamycin-sensitive phosphorylation sites of 4E-BP1. The study also shows that RAFT1 phosphorylates p70S6k on Thr-389, which is essential for S6 kinase activity. Mutation of Thr-389 to alanine significantly reduces S6 kinase activity and prevents serum stimulation. RAFT1 phosphorylates 4E-BP1 on Thr-36 and Thr-45, which blocks its interaction with eIF-4E. Mutation of these sites to alanine causes 4E-BP1 to constitutively bind to eIF-4E, mimicking the effects of rapamycin. These findings indicate that RAFT1 plays a critical role in regulating the interaction between 4E-BP1 and eIF-4E, which is essential for cap-dependent translation. The study also highlights the importance of RAFT1 in the rapamycin-sensitive signaling pathway, which is involved in regulating protein synthesis in response to growth factors. The results suggest that RAFT1 is a key regulator of translation, and its phosphorylation of p70S6k and 4E-BP1 is essential for the proper functioning of the pathway. The study provides important insights into the molecular mechanisms underlying the regulation of protein synthesis and the role of RAFT1 in this process.