Macromolecular interactions in protein synthesis: the interaction of tRNA with its biological partners (aminoacyl-tRNA synthetase,

The accessibility of phosphates towards ethylnitrosourea was studied in tRNA/aminoacyl-.tRNA synthetase complexes and in the ternary aminoacyltRNA/EF-Tu/GTP complex. When the tRNA is complexed to aminoacyl-tRNA synthetases, several phosphates are protected against the alkylation agent, the protection patterns varying according to the tRNA/aminoacyl-tRNA synthetase system. However in all cases phosphates of the anticodon stem are protected. In the ternary aminoacyl-tRNA/EF-Tu/GTP complex, no protection of phosphates is observed. On the contrary, the accessibility of several phosphates is increased, suggesting a structural rearrangement of the tRNA induced by complex formation. To identify ribosomal components involved in thgeptidyl-tRNA binding site two approaches have been investigated : (i) tRNA molecules have been prepared in which cytidine has been randomly converted into 4-thiouridine by pr*ssurized hydrogen sulfide. Direct irradiation at 335 nm of N-Ac-Phe(S U)tRNA(Phe)/PolyU/70S ribosome complex induced covalent crosslinking of the Phe-tRNA(Phe) molecules exclusively to protein SlO in the 30S subunits. (ii) Photochemical crossl inking of ribosomal P site bound Ac-Val-tRNA(Val) to a region near the 3-end of small subunit RNAs from prokaryotes and eukaryotgs occurs,5 via cyclobutane dimer formation, between the 5-anticodon base cmo U34 or mo U34 of tRNA and Cl400 of E.coli 16S rRNA or Cl626 of yeast 18S rRNA. The crosslinking site is in the centre of a sequence which is evolutionarily conserved, has a single stranded structure and is located at the ribosomal subunit interface.