Trichosanthin (TCS) is a type Ⅰ ribosome-inactivating protein and an RNA N-glycosidase that depurinates the A4324 at the α-sarcin-ricin loop of the 28S rRNA.We hypothesize that TCS requires to first dock on the ribosome before carrying out its catalytic activity.Previously,we have shown that TCS interacts with human acidic ribosomal P proteins,which constitutes the lateral stalk of eukaryotic ribosome.Deletion mutagenesis showed that TCS interacts with the C-terminal tail of P2,which sequences are almost invariant in P0,P1 and P2.The P protein binding site on TCS was mapped to the C-terminal domain by chemical shift perturbation experiments.