Proteomic analysis of mTOR inhibition- mediated phosphorylation changes in ribosomal proteins and eukaryotic translation initiation factors

Dear Editor, The mammalian target of rapamycin （mTOR）, as a critical energy sensor and cell-growth regulator, controls protein synthesis, autophagy and many important cellular processes through forming functional distinct complexes, mTORC1 and mTORC2, mTORC1 that is sensitive to rapamycin, regulates cell growth and protein synthesis, while mTORC2 that is insensitive to rapamycin, regulates cellular metabolism and the cytoskeletal organization （Gingras et al., 2001; Hay and Sonenberg, 2004）. Translation initiation is the rate-limiting step in protein synthesis, which proceeds through a multi- step process that can be divided into three major steps. First, eukaryotic translation initiation factor 2 （elF2） binds with GTP and methionyl-tRNA to form the ternary complex, which further binds to 40S ribosomal subunit with the help of elF1, elF1A, elF3 and elF5 resulting the preinitiation complex （PIC）. Second, the PIC binds to mRNA which is unwinded by the elF4F complex （including elF4E, elF4G, elF4A, elF4B）.