TRANSFER-RNA DOCKING PAIR MODEL IN THE RIBOSOMAL PRE-TRANSLOCATIONAL AND POST-TRANSLOCATIONAL STATES

A consensus has been reached that the conformation of the anticodon-co don interactions of two adjacent tRNA molecules on the ribosome is a S undaralingam-type (S-type). Even if it is kept to the S-type, there ar e still various possibilities, Various experimental data have been sup porting an idea that the conformation of A-site tRNA is different from that: of P-site tRNA, Those data as well as the recent result of Brim acombe and co-workers that U20:1 of lupin tRNA(m)(Met) bound to the A- site was cross-linked to a region, 875-905, of 23S rRNA in combination with the other recent findings of Nierhaus and co-workers about the s pin-contrast method of neutron diffraction of the ribosome and the bet ter accessible nucleotide patterns of phosphorethioated tRNAs on the r ibosome have led to a new tRNA docking pair model, in which the highly conserved G18 and G19 of D-loop in A-site tRNA and C56 and C61 of T p si C-loop in P-site tRNA base pair along with the conventional base pa irs of adjacent codon-anticodon interactions, This A-P tRNA pair model can be translocated to the P-E tRNA pair model without changing the c onformation except the ACCA termini, keeping the position of the growi ng nascent polypeptide chain.