A SPARSOMYCIN-RESISTANT MUTANT OF HALOBACTERIUM-SALINARIUM LACKS A MODIFICATION AT NUCLEOTIDE U2603 IN THE PEPTIDYL TRANSFERASE CENTER OF 23-S RIBOSOMAL-RNA

Sparsomycin, a broad-spectrum antibiotic, acts at the peptidyl transfe rase centre of the ribosome, stabilizing peptidyl-tRNA binding at the P-site and weakening ternary complex binding. A sparsomycin-resistant mutant was isolated for the archaeon Halobacterium salinarium and show n to lack a post-transcriptional modification of U2603 (Escherichia co li numbering U2584), which is a universally conserved uridine base loc ated within the peptidyl transferase loop of 23 S rRNA. This mutant al so exhibited altered sensitivities to the peptidyl transferase antibio tics anisomycin, chloramphenicol and puromycin. Several lines of evide nce indicate that the unmodified uridine base lies within the P-substr ate site of the peptidyl transferase centre. (C) 1996 Academic Press L imited