[Structural elements of 80S ribosomes located near the 5'-region of the mRNA-binding center]. / Strukturnye élementy 80S ribosomy, raspolozhennye vblizi 5'-oblasti mRNK-sviazyvaiushchego tsentra.

Affinity labeling of 80S ribosomes with 4-(N-2-chloroethyl-N-methylamino)benzylmethylphosphoramides of oligoribonucleotides [32P]AUGUn--mRNA analogs--was studied in three model complexes: 80S.ClRCH2N(CH3)-pAUGU6.Met(Phe)2-trRNA(Phe), 80S.ClRCH2N(CH3)pAUGU3.MetPhe-tRNA(Phe), and 80S.ClRCH2N(CH3)-pAUG.Met- tRNA(Met). Two of these complexes imitate the posttranslocational state of 80S ribosomes. Small subunits were labeled preferentially; both 18S rRNA and ribosomal proteins were modified by the mRNA analogs. The relative modification extents of proteins and rRNA depended on the length of the reagent oligoribonucleotide moiety. Extension of the latter resulted in decrease in the relative extent of 18S rRNA modification from 95 a to 16% (for proteins, increase from 5 to 84%, respectively). Fragments of 18S rRNA containing cross-linking sites were identified using blot hybridization. In all cases, fragment 976-1164 was found to be modified. In the case of ClRCH2N(CH3)pAUGU6, labeling occurred also within fragments 593-673 and 1748-1869. Analysis of the modified proteins revealed that proteins S14/S15 were labeled with all three reagents and were the single target of modification with ClRCH2N(CH3)pAUGU6. Proteins S3/S3a, S6, and S16/S18 were modified only with ClRCH2N(CH3)pAUGU3; protein S20 only with ClRCH2N(CH3)pAUG; and proteins S5 and S17 were labeled with both reagents (n = 0, 3).

[Interaction of mRNA analogs--oligoribonucleotides AUGU3, AUGU6 and (pU)6 with 80S ribosomes from human placenta in the presence of related tRNA and a protein-synthesizing system]. / Vzaimodeistvie analogov mRNK--oligoribonukleotidov AUGU2, AUGU6, and (pU)6 s 80S ribosomami iz platsenty cheloveka v prisutstvii rodstvennykh tRNK i beloksinteziruiushchei sistemy.

Binding of oligoribonucleotides AUGUn (n-3 and 6) and (pU) to 80S ribosomes from human placenta in the presence of cognate tRNAs and a "ribosome-free" protein-synthesizing system from rabbit reticulocytes has been studied. The binding of the mRNA analogues resulted in formation of stable post-translocational complexes (which may be easily isolated by centrifugation in sucrose density gradient): 80S.AUGU3.MetPhe-tRNA(Phe); 80S.AUGU6.Met(Phe)2.tRNA(Phe); 80S.(pU)6.(Phe)2-tRNA(Phe). In these complexes the ratios of the bound ligands are close to the theoretically expected values. Comparison of the results obtained with the previously reported data on nonenzymatic binding of oligouridylates and Phe-tRNA(Phe) to 80S ribosomes lead one to the conclusion that translation factors significantly stabilize the complexes of tRNA with 80S ribosomes and oligoribonucleotide templates.