[Affinity modification of Escherichia coli ribosomes in the region of the mRNA-binding center by a heptauridylate analog bearing a chemically active group at the 3' end].

4-(N-2-chloroethyl-N-methylamino)-benzaldehyde acetyl derivative (RCL-derivative) of hepatauridylic acid was used to localize the structure organizing the mRNA-binding site of ribosomes. This derivative; like a free oligonucleotide, stimulates the binding of [14C]phenylalanyl-tRNA to ribosomes and effectively alkylates ribosomes, mainly the 30S subunit within the specific complex. The alkylation being completely inhibited by preincubation with polyuridylic acid, suggests that the chemical alteration occurs near the mRNA-binding site. Both rRNA and proteins undergo modification in the 30S subunit (15 and 85% of the total 30S subunit, respectively). The radioactive marked was found in fractions of proteins S18, S9 and S1.