Mutations at position A960 of E-coli 23 S ribosomal RNA influence the structure of 5 S ribosomal RNA and the peptidyltransferase region of 23 S ribosomal RNA

The proximity of loop D of 5 S rRNA to two regions of 23 S rRNA, domain II involved in translocation and domain V involved in peptide bond formation, is known from previous cross-linking experiments. Here, we have used site-d irected mutagenesis and chemical probing to further define these contacts a nd possible sites of communication between 5 S and 23 S rRNA. Three differe nt mutants were constructed at position A960, a highly conserved nucleotide in domain TI previously crosslinked to 5 S rRNA, and the mutant rRNAs were expressed from plasmids as homogeneous populations of ribosomes in Escheri chia coli deficient in all seven chromosomal copies of the rRNA operon. Mut ations A960U, A960G and, particularly, A960C caused structural rearrangemen ts in the loop D of 5 S rRNA and in the peptidyltransferase region of domai n V, as well as in the 960 loop itself. These observations support the prop osal that loop D of 5 S rRNA participates in signal transmission between th e ribosome centers responsible for peptide bond formation and translocation . (C) 2000 Academic Press.