AFFINITY MODIFICATION OF 80S RIBOSOMES FROM HUMAN PLACENTA WITH MESSENGER-RNA ANALOGS - OLIGOURIDYLATE DERIVATIVES WITH AN ALKYLATING GROUPAT 3'-END

'-O-[4-(N-2-chloroethyl-N-methylamino)]benzylidene derivatives of olig oribonucleotides (Up)5U [P-32]pC and (Up)11U [P-32]pC were used for af finity modification of 80S ribosomes from human placenta in the presen ce of related Phe-tRNA(Phe). The derivatives were still capable of the nonenzymatic tRNA(Phe)-dependent binding to 80S ribosomes and, within appropriate complexes, they were joined covalently to 40S subunits (p rimarily to 18S rRNA). The sites of covalent binding of both mRNA anal ogs were identified by blot-hybridization of the modified rRNA with re striction fragments of the appropriate rDNA and localized at positions 1610-1747 and 1748-1865 of 18S rRNA. These 18S rRNA fragments are loc ated at the 3'-terminal part of the molecule in the highly conserved r egion of rRNA secondary structure in small subunits of eukaryotic ribo somes.