STRUCTURAL ELEMENTS OF 80S-RIBOSOME ADJACENT TO THE 5' SIDE OF MESSENGER-RNA-BINDING CENTER

hloroethyl-N-methylamino)benzylmethylphosphoamides of oligoribonucleol ides [P-32]pA-UGU(n)(n = 0, 3, 6) were used for affinity modification of 80S ribosomes from human placenta. The resulting complexes [80S-ClR CH(2)N(CH3)pAUGU(6)-Met(Phe)(2)-tRNA(Phe) and 80S-ClRCH(2)N(CH3) pAUGU (6)-Met(Phe)-tRNA(Phe)] imitated the posttranslocation state of the 80 S ribosome. The oligoribonucleotides were attached primarily to the 40 S subunit. The relative extent of modification of 18S RNA and the prot eins depended on the length of the oligonucleotide chain. As the latte r increased, the relative extent of modification of 18S RNA dropped. T he attachment sites were identified within the 976-1164 region of 18S RNA by blot hybridization. The alkylating derivative ClRCH(2)N(CH3)pAU GU(6) was also attached to the 593-673 and 1748-1869 fragments. It was shown that the S14 and S15 proteins are modified by ah three reagents ; S16 and S18 proteins were modified only by ClRCH(2)N(CH3)pAUG, where as the S5 and S17 proteins were alkylated by both reagents (n = 0, 3).