FUNCTIONAL IMPLICATIONS OF RIBOSOMAL-PROTEIN L2 IN PROTEIN-BIOSYNTHESIS AS SHOWN BY IN-VIVO REPLACEMENT STUDIES

The translational apparatus is a highly complex structure containing t hree to four RNA molecules and more than SO different proteins. In rec ent years considerable evidence has accumulated to indicate that the R NA participates intensively in the catalysis of peptide-bond formation , whereas a direct involvement of the ribosomal proteins has yet to be demonstrated. Here we report the functional and structural conservati on of a peptidyltransferase centre protein in all three phylogenetic d omains. In two replacement studies show that the Escherichia coli L2 p rotein can be replaced by its homologous proteins from human and archa ebacterial ribosomes. These hybrid ribosomes are active in protein bio synthesis, as proven by polysome analysis and poly(U)-dependent polyph enylalanine synthesis. Furthermore, we demonstrate that a specific, hi ghly conserved, histidine residue in the C-terminal region of L2 is es sential for the function of the translational apparatus. Replacement o f this histidine residue in the human and archaebacterial proteins by glycine, arginine or alanine had no effect on ribosome assembly, but s trongly reduced the translational activity of ribosomes containing the se mutants.