[Study of the poly(U)-dependent interaction of tRNA(Phe) with the P-site of Escherichia coli ribosomes by chemical modification with nitrosoethylurea].

The accessibility of phosphates in E. coli tRNA(Phe) bound to E. coli ribosomes and 30S subunits for attack by an alkylating agent ethylnitrosourea was studied. The experimental technique allowed us to investigate a part of the molecule between N-11 and N-72. Being bound to the poly(U)-programmed P site of 30S subunit, tRNA(Phe) reveals protection in a discrete region including phosphates 23-44. This region corresponds to the hairpin formed from the anticodon arm and the adjoining 3' strand of the D stem and the variable loop. On the P site of 70S-poly(U), additional protection was observed in a region between N-45 and N-63. This region corresponds to the extra loop and T stem, and reveals a fine structure of protection: protected phosphates in positions 45-49, 51, 54-55, 58-61, and 63 alternate with unprotected ones in positions 50, 52-53, 56-57 and 62. We conclude that ethylnitrosourea can be used for detailed study of tRNA-ribosome contacts.