Identification of molecular interactions between P-site tRNA and the ribosome essential for translocation

Translocation of the tRNA-mRNA complex is a fundamental step in the elongat ion cycle of protein synthesis. Our studies show that the ribosome can tran slocate a P-site-bound tRNA(Met) with a break in the phosphodiester backbon e between positions 56 and 57 in the T psiC-loop. We have used this fragmen ted P-site-bound tRNAMet to identify two 2 ' -hydroxyl groups at positions 71 and 76 in the 3 ' -acceptor arm that are essential for translocation. Cr ystallographic data show that the 2 ' -hydroxyl group at positions 71 and 7 6 contacts the backbone of 235 rRNA residues 1892 and 2433-2434, respective ly, in the ribosomal E site. These results establish a set of functional in teractions between P-site tRNA and 235 rRNA that are essential for transloc ation.