[Affinity modification of 40S ribosomal subparticles from human placenta with mRNA analogs--AUGUnC oligoribonucleotide analogs with an alkylating group at the 3'-end].

Using 2',3'-O-[4-N-(2-chloroethyl)-N-methylamino]benzylidene derivatives of AUGUn[32P]pC (mRNA analogues), affinity labelling of human placenta 40S ribosomal subunits has been investigated in model initiation complexes obtained in the presence of the ternary complex eIF-2.GTP.Met-tRNA(fMet). The regions of 18S rRNA labelled with these mRNA analogues were identified. The main targets of 18S rRNA alkylation by the derivative of AUG[32P]pC were located within positions 1610-1747 and 1748-1869. The site of covalent attachment of AUGU3[32P]pC derivative to 18S rRNA was found within positions 593-673. Taking into account the data on labelling of human placenta ribosomes with the same derivatives of oligourydilates obtained previously, the conclusion was made that the arrangement of the codon U3 in the mRNA-binding centre of the initiation complex 40S.AUGU3[32P]pC derivative.eIF-2.GTP.Met-TPHK(fMet) differs from the arrangement of the same codon at the A-site of the complex imitating the pretranslocation state of ribosomes.