Identification of 50S components neighboring 23S rRNA nucleotides A2448 and U2604 within the peptidyl transferase center of Escherichia coli ribosomes

The 23S rRNA nucleotides 2604-12 and 2448-58 fall within the central loop o f domain V, which forms a major part of the peptidyl transferase center of the ribosome, We report the synthesis of radioactive, photolabile 2'-O-meth yloligoRNAs, PHONTs 1 and 2, complementary to these nucleotides and their e xploitation in identifying 50S ribosomal subunit components neighboring the ir target sites. Photolysis of the 50S complex with PHONT 1, complementary to nts 2604-12, leads to target site-specific photoincorporation into prote in L2 and 23S rRNA nucleotides A886, A1918, A1919, G1922-C1924, U2563, U258 6, and C2601, Photolysis of the 50S complex with PHONT 2, complementary to nts 2448-58, leads to target site-specific probe photoincorporation into pr oteins L2, L3, one or more of proteins L17, L18, L21, and of proteins L9, L 15, L16, and 23S rRNA nucleotides C2456 and psi 2457. Chemical footprinting studies show that 2'-O-methyloligoRNA binding causes Little distortion of the peptidyl transferase center but do provide suggestive evidence for the location of flexible regions within 23S rRNA. The significance of these res ults for the structure of the peptidyl transferase center is considered.