[Affinity modification of 80S ribosomes from human placenta with mRNA analogs--derivatives of oligouridylates with and alkylating group at the 5'-end].

Affinity labelling of 80S ribosomes from human placenta with 4-(N-methylamino-N-2-chloroethyl)benzylmethylphosphoramide derivatives of oligouridylates pUn (n = 3, 4, 6, 12) bearing 5'-32P-label was studied. Complexes of these derivatives with 80S ribosomes where codon-anticodon interaction took place either in P-site (in the case of pU3-and pU4-derivatives), or in P- and A-site simultaneously (in the case of pU6- and pU12-derivatives) were obtained in the presence of Phe-tRNA(Phe). All the reagents modified only the 40S subunit. The extent of 18S rRNA modification by pU3-, pU4-, pU6- and pU12-derivatives as a fraction of the total modification extent of 18S rRNA and proteins in the 40S subunit equaled 96, 93, 24 and 4%, respectively. The pU4-derivative was covalently attached at positions 976-1061 and 1058-1164 and pU12-derivative was covalently attached within regions 976-1061, 1058-1164, 593-673 and 1748-1869 of the 18S rRNA. By means of the primer extension technique, modified bases in 18S rRNA were determined to be: A-1023, C-1026, A-1027, A-1058, G-1059 for pU3- and pU4-derivatives and A-1058 for pU6-derivative.