A, PhAXA and structure of ATP crosslinker probe 1. B, HEK293T cells transfected with WT or 3XFLAG phosphosite-to-Cys mutant 4E-BP1 constructs were lysed, treated with 1 or ATP and analyzed via Western blot. A minimal mass shift is observed due to the negligible size of FLAG-4E-BP1 relative to mTOR. C, PP242 (10,000–1 nM) and D, rapamycin (100 nM) inhibit the crosslinking of mTOR to the T46C 4E-BP1 in the presence of 1.